340 Piston identification. Silvolite?

Thanks for all the geat info, I measured (with a Harbour Freight micrometer) they came out to 1.230 and with adding the .492 came out to 1.722, so from above if they are 8.5-1 would it be a big difference to run a better piston, also what’s the ideal for a hot street car 10.5?
Oh yeah! A BIIIG difference. 'Hot street' is a bit variable of a term but you are getting into the right ballpark. What heads are you going to use?