All ya have to do is take a 235/261 head and take a look at the very poor combustion chamber design.It's hard to do any improvements without a flow equipment or a lot of past experience,no one on this site past or present has that experience.According to Patrick Dykes,you can spend a lot of money and time reworking the head and not end up much better than a stock head.Leo Sanducci ,before he raced 292's,ran 235 and 261's,he says the same for a street engine.
They used to make wierd domed pistons for 235's to raise compression,not available anymore.Using flat top pistons,milling the block as necessary for zero deck height,mill the head about .060 that,watch the intake valve to piston clearance,and wind up with 9-1 actual compression.This is more or less the maxiumum compression these engines will tolerate on the current pump gas.
The so called Caddy piston conversion requires some expensive and possible suspect crank machining to get more cubic inches,but your still dealing with the poor head design.
You can spend thousands of bucks on these engines and wind up with 200 or so hp.
If ya want real HP in a vintage engine,the 302 GMC is the way to go.The same money spent will give 250 HP at reasonable rpm on the GMC.
I had a great running 261 in my 37 Chevy pu,replaced it with a GMC 302 in the same state of tune,the difference in power is really noticable.That's my opinion from actual experience building these old lumps.
