If you use a small cam like the Comp Cams early magnum series or similar with under .500 net lift the stock valve springs should work fine scope
As far as replacing those two stock OEM street wedge pistons look under the bottoms of the pistons and post the casting numbers on here, I may have one good used one in my shop luck
Are you going to use a stick shift tranny or a automatic tranny?
Which carb type and part number are you wanting to use? I use to race a Max wedge car with AFB carbs. and I have a lot of old carb. kits left over so I may be able to make up enough gaskets and parts so you can freshen yours thumbs work scope
Tell us what you want your motor to do as far as street, street and strip or what?

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)