sorry about my late reply, been busy working on my house.
Engine sits in a 1965 impala, bigger engine is not possible because of the safety inspection, more power is because there is no mentioning on hp on the papers.
SNIP
Ps no new engines will be use because i want a carburated car and the new V6 are all injection
The 2006/2009 Saab SUVs had a GM DOHC 4.2L inline 6 (same size as your 250), if you built an carb intake for it (intake flanges are available) and put a 4bbl carb on it, you would get 270ish HP with out the turbo. The ignition can be run by a stand alone ignition controller so no need to run the factory PCM.
Add a turbo later and get 400+HP
