Unless you are going for a big cam,
1.save money on the 500,
and lose the potential of 70 hp that you'd never get anyway,
or
2. spend, oh, 150 extra on a 465, then 200 on the alloy welding, and maybee 100 ping on getting the air cleaner sorted.
The advantage is that part throttle economy on a 4-bbl is always better than a 500 cfm 2-bbl. You'd maybee save 2 mpg at 100 km/h if you could run it lean enough, and if you did 20 000 open road km per year, you'd save about 250 bucks a year on fuel if you used about 2800 litres each year. In short, it may take about 2 years to save the extra 450 bucks.
The 465 road.
The 465 won't fit unless you do about 200 bucks worth of alloy welding and machining. So if the dollar is the kingmaker, don't get a 465. In addition to it being expensive, it'll need those mods.
The plusses are very significant. All the mods are suggested in earlier posts by Mustangaroo and co in there posts. The guys in the 2V US guys have problems with the spring towers hitting the carb unless its spun around the right way. Down under, we have problems finding air cleaners which fit, since the Stromberg 2-bbl stocker is like 39 mm thick at the air cleaner.
If you do the mods to fit it, the 4-bbl will work and fit in the same space with no real issues. In addition to the alloy welding, you have to use the stock air cleaner, and find a top and bottom adaptor to allow the thing to sit snug. The 2V mixed with a welded section of the 302C base cut should be okay, and then just find out how to hold the stock 2V lid down. It must have a curved top, or the Holley carbs will suffer.
It's not a simple swap, but there is info from the guys here, and we know from other historical accounts, the 465 can make 280 hp with ease. The 500 cfm (really a 354 cfm carb) 2-bbl runs out at 220 hp. There are ways to turn at 354 cfm 2-bbl into a 450 cfm carb using the Demon or Bary Grant versions, with 62.5 thou over throttles and venturis, but its more work and expense than just getting the 465 cfm carb.
Finally, the 465 cfm 4-bbl is the carb in the Commodore Challange Cup, little 253's hit the 280-300 hp mark on a regular basis.
See, both have merrits. My misses hates me because she thinks I just make an ass on analysing stuff. Point is, either one will work okay, and wahtever you do, you can't loose!
