I've seen your work, and believe in your efforts, brother, but it's too much to ask first up. Mainly because the 250 isn't just a big 200, its a totally new block resting under the stock log head!
You need to do it on a broken 250 or 200 first, and then have a go on yours. It's a bit like a karate move...must be premeditated and worked on in advance so that when the situation comes up, it's an automatic manouvre.
The US 250 runs an extensively altered crank gear, and a chain which is different to the US 200. The cam gear is similar but not the same, IIRC.
Tools like a three leg crank damper remover (The damper is a 250 spec item, much bigger than the 200 ones). A new damper/balancer is likely to be needed. If the elastomeric seal is cracked, the heavy out ring will fly off the inner balancer next time you do a hard run with your new wild cam. The balancer needs to be torqued up properly to the factory spec for a 250. My X-flow 250 in my Falcon has was running for a year without a crank bolt, but a 250 balancer soaks up a heap of crank vibration, and just a short run has it very hot. It's heat the breaks down the elastomeric rubber, not vibration.
In Aussie and Argie blocks, all the 188/221 and Oz 250's run a 200 cube chain but with an extra link. The US 250, however, is totally beafed up with a thicker front snout which means pieces don't interchange. The cam position has space for a stroke even bigger than the mamoth 3.91" it has. (Ford's Canadian Windsor plant may have been planning to take the block out to well over 250 cubes in the 70's!)
The best bet is to get the new 250 timing chain, thrust washer and new dowel which pegs the cam in. New neoprene front cover seal, and a gasket. Despite what some say, I've heard that well worn stock cam bearings are just fine, so its a straight removal of the distributor and the so called 'macorni drive' hexagonal oil pump drive, cam and crank gear, and camshaft and lifters . This is very difficult, sometimes impossible to do on an old engine with the head still on. The trick is to use a pice of high carbon 2 mm gauge wire with a sharp 45 degree bend on the inside to flick the stock lifters up over the carbon ridge that forms above the lifter gallery.
The hex drive should be replaced with a new US market 250 item. The drive is much longer than the US 200, and also 3/8" longer than the Aussie 250. It's a specific unit to the US 250, which again shows that the Dearborn design team had done a huge amount of ovetime on the US 250.
Since the Ford team have done such a huge amount of work on it, plan a cam instillation only after you've done a strip and rough rebuild.
Get the tools, new parts, get an idea of how to do it on a scrap engine, and then go wild yourself.
If you are going to the trouble to run a new cam, find out what size the stock 250 US keyway is, and order a couple of -2 and +2 degree offset versions. The stock cam can be advanced very sucessfully on this huge engine, and degreeing the cam to the specs is a must. Ford has very wide tollerances on the stock crank and cam dots, and they can be a mile off.
Just like the nasty 100 thou short fall in piston height.
If you want some degreeing info there are some website details that cover it.
Hope all this prattle isn't makin you anxious, because a 250 is dead easy to cam swap. I did it in 30 minutes on my 200 Falcon engine. It's just that a few parts not quite right can scr@w up a nice weekend!
