I'm partial to 4.1's, its the best enginew round town, and the best cruiser ever. Although they are certainly not perfect. They have typical big Cleveland engine problems of extra weight (460 pounds dressed without air con and power steering vs 385 pound max for 3.3) but then still have thinwall related bore constraints
A few cuts,
and it'll fit, piece of cake
Regards the best combination, fix the the worst thing first. The bug bear is the 103 thou piston shortfall, which is only fixable by a block deck (bad idea, as on 250 engines, it often causes cracks to apear around the front cylinder head to block bolt holes, causing hairline cracks in no 1 cylinder commonly), or a set of forged EL2/AU/BA/BF/FG Falcon OHC six rods, or 2.5 HSC Taurus or Topaz. They are 6.06" and 6.00" centre to centre respectively, and fix the shortfall, but you then have to use a thick composite head gasket which doesn't ledge over the block and a decked aftermarket piston...the best is the 1.5" deck 255 Ford V8 replacement as its about 8cc. If you can machine them down to 1.454- 1.460", you'll have about the best small six combo on the planet. The old 229/305 Chev TRW or Keith Black forged piston is 12cc, and can be decked from 1.536 down to 1.454 with ease, but the wrist pins then need to be taken out 16 thou to 0.927". And it needs a 56 thou overbore to fit a 250 block, 3.736 vs 3.680". Each option has its pro's and cons, but the piston shortfall at top dead centre is a huge power looser, more than 10% due to an inability to carry a high compression ratio. Just dropping a 48 cc head on a stock 250 which had 59 to 62 cc head doesn't yield any more power, as it tries to detonate early due to the heated anular edge.
The second problem with all Cleveland Ohio made Ford sixes, is that the cylinder walls are too thin for real overbores, making high performance mods hard work. Often, people, like
powerband and others, have had plenty of nice years running a good old Jeep 258 pistons (58 thou over size), but most times a 250 block was as thin as 120 thou at the thrust faces when cast, and with age, it can drop to 90 thou before you give them an overbore. So best options in my book are making sure its not got winter cracks if its from a cold zone in the US, and if its free from cracks, then concentrate on getting the compression up to 9.5:1 next engine rebuild.
As things stand now, your constrained by a carb which is fine for a 99 hp net low compression plodder. If you remove EGR, AIR, and the other 10 integrated emmissions devices you won't be any further ahead, but it'll probably look cleaner in a 64 engine bay.
Given that internal mods aren't on your radar yet, my pick is the direct mount conversion, and the Holley 350 cfm carb. Jetting is best kept down to 62-64 jets, with 6.5 power valve, and winding a silver 10 amp fuse through both the power valve channel restrictions. (350 Holleys are set up for big V8's, and the whole basic jetting, including all the hard fuel and air corrector channels, are sized for 351/352 to 390, and a six with a 350 Holley always runs richer than it would if Holley had a calibration for a 2 bbl 250).
Hooker dual out headers are best, and if you are using a high mount right hand air con unit (like Sanden or its variants), then you might need to shift the a/c compressor out a 1/4 to 1/2" to clear the larger header tubes. If its low mount, then you should be okay.
Trans is easy...wide ratio RUC/SROD or any wide or close Ford v8 Toploader except the Liberty 429, or the SR from X-shell Granda/Fox Body 3.3 stick shifts. Close ratios (2.32, 1.69, 1.29, 1:1) are the set up if you have 3.5:1 gears...the 250 is a real torque monster and laps up high gearing like a Clydesdale.
Best diff ratio is 3.20 to 3.25:1, best gearing 2.78, 1.86, 1.36, 1:1. That always works well with a 2 barrel 250, with only a marginal loss in economy. Close to it is the RUC or SROD, which were 3speed plus overdrive boxes with 2.95, 1.69, 1.29, 0.79, I think. That works real well with 3.20 to 3.50 diff ratios.
If you want an auto, follow Jacs Crossflow Chronicals, and try an 89-92 AOD from a truck 5.0 LTD...with the factory Mustang 5.0 HO 2350 rpm stall converter and 3.5 or even 4.0 gears, a 4.9 164 teeth neutral balance flexplate, and forget the fact that its 165 pounds, or 65 pounds heavier than a C4. It's a great box when the diff ratios are numerically high, and all you have to do is make sure there is 1/8 inch slack at idle and 1.75" of total pullout on the throttle cable at wide open throttle with the engine having just been run but turned off. Stock stall is the standard Ford 1650 rpm stall, and it kills most modifed engines with diff ratios in the 2.79/2.83/3.00/3.20/3.25 range. To make an AOD work,it needs a 3.45:1 down to 4.11 diff to cruise nicely on locked up overdrive top.
65 extra pounds in a gearbox, 75 or more in the engine, a better 8" diff, air con, power steering, and it all adds up to 25% more capacity, but 6 or 7% more weight. People then look at air con because a 4.1 Falcon is such a cruisy car, and power steering, because its a mutha to steer with all that extra weight up front. A stock 250 never, ever got 25% more power than the same year 200 due to the carb, log head and awfull piston shortfall, so mostly,without modifaction, a 250 is 25% more torquey down low from idle to about 3500 rpm, and then it only makes 6 to 7% more power, just enough to keep up with a 6 to 7% weight increase. If you check any drive report, a manual 4 speed 200 will beat most loaded auto 250's, all else being equal.
Hi FSD.The more that I read in this thread the more that I think about a couple of sayings from the "Way Back Machine".
x2 
