Sharing my personal experience with 500-block, 650 cylinders/pistons, factory 500cc cyl head, and factory Weber 24 carb.
I fully appreciate that this thread is several years old so I don’t expect any responses....but if I get some, all the better.
I have a 69’ 500 block/crankcase with the aforementioned 650 cyl/pistons with spacers installed and have just recently started the engine for the first time following a 7-year storage period.
Having fully forgotten what I did when I built this engine it’s taken me a while to piece together what I have in/on it but....so far I can confirm the standard 500 crankcase/block (thermal coated for heat dispersion), and the aftermarket 650 pistons and cylinders. I can also confirm that I have the original 4240095 cylinder head for the 500cc. I also have the original Weber 24 carburetor on there....which to my surprise has apparently been running very rich for the motor (the plugs were covered in carbon soot).
Out of curiosity, I tested my compression and repeatedly came up with 170-180 psi on both cylinders. Testing was conducted with both spark plugs removed and with the carburetor held wide open. Yet despite this high compression ..... i have no memory of the car running poorly or with any detonation.
I plan to test drive the car in the next month or two depending on weather (we’ve had exceedingly warm temperatures here in Washington DC for this time of year). Assuming the test and tune drives go well.....I’m planning on attempting to install a small supercharger on the engine. I suspect that with my high compression and factory heads and carb,....I’ll be asking for all kinds of headaches and upgrades but.....”even the mighty oak, was once a little nut that just held its ground”.