No problem, I thought everyone was tired of reading this......
Start with a decent 413 shortblock, remove forged 3.75" crank and sell it to someone who wants it more than you do.
Remove pistons from rods, keep the rods and recycle the pistons.
Scrounge some standard size 383 pistons for low $. When I first came up with this idea you could buy cast low compression 383 pistons for less than $100 a set on the 'bay. Things may have changed, I haven't checked lately.
Optional: Sonic-check the block. We're going to bore it out from 4.1875 to 4.25, a little over 0.060" or 1.5mm. Here in the land of round doorknobs, 413 block prices are low. In France, things may be different. Most 413 blocks should handle a 0.0625" overbore with no problem.
Buy a 4.15" stroke crank for 413/440. If it's 4.15 or 4.125 or 4.14 doesn't matter. This is not a zero deck engine anyway.
Balance the assembly, shouldn't be too hard as everything is close to stock weights. If you have to use some external balance don't worry about it, just do it. This is a low-rpm torque motor.
Mount pistons on rods.
Install rotating assembly, checking for clearance. Usually no problems but it never hurts to check. In case of interference, fearlessly but carefully grind on the block.
Use a decent cam, I like the Comp XE275HL. I am probably 2 years out of date on that as I have been out of the game for a while. Using a shorter-duration cam isn't recommended.
Use open chamber heads with larger valves and port the bowls like you can find online either here or other places. I suggest the latest 452 heads, the ones with a numeral "1" cast onto the end. But an a pinch, any open chamber head will do. Keep in mind that inexperienced porters have better luck with 346, 213 or 452 heads. The 92cc chambers will give compression of nearly 10:1 so premium gas is probably wise. Thicker head gaskets may be better here.
As you're using stock rods (wimpy 3/8" rod bolts) and a long-stroke crank with stock weight pistons, limit rpm to 5000.
I'd suggest a Holley Street Dominator with a big Thermoquad or else an Edelbrock Perf RPM with a 750 Holley 3310.
End result is a 400 hp 472 that should have incredible torque and be decently reliable. It will force you to do suspension work to put all that power on the ground.
Good cooking!
R.
