The pistons I use in 496 combos are SRP 139832 which are full dome and are 2618 alloy. It says so in the instructions that comes in the box and on the site
www.srp.com. I have used these in several engines in the last 3 years with no complaints.
But the flat top and mini dome ARE 4032 alloy. That alloy is designed for street/strip use. It allows for tighter cylinder wall clearances and is stronger than a hypertecnic cast piston. 4032 is not recommend for alcohol use either.
But I did build a 421 alcohol SBC with dome 4032 pistons and it has over 200 runs on it now with no complaints, running 5.90s.
I just don't want people to think all BBC SRP pistons are 4032.