Thinking about your questions last night and I think the 3.7/4.7 pistons may not be your best option. I really think you will struggle to get your compression down low enough, there isn't a lot of meat on the piston crown for too much cutting of valve reliefs and combustion bowl.
I think another better option may be the Mitsubishi 6g74 piston, have a look at the DOHC variant of the 6g74. They have a bowl and valve cutouts already in them. Whether the cutouts line up with your cosworth valves I have no idea. You will also have to do your own research on what your compression would end up being. These pistons have a smaller gudgeon pin, so the rod small end will need bushing. I did look at these pistons when I was deciding how I was going to build my 3.5.
Last edited by Stroker; 05-03-2019 at 06:47 PM.