The 702 heads are not real good flow heads. Will require much labor $$$ to work. Hard seats with 2.19-1.88" valves will help flow and streetability. But, The small chambers, which you need on a 396, shroud the valves. Also will need valve spring pocket work to install springs for roller lift specs $$$.
Add the basic machine work $$$ and parts to make these old heads usable and you have a major investment in mediocre heads.
+.300 lifters are for later blocks. Go with steel retainers.
Then you get into pistons. Only basic rebuilders stuff is stocked or even available by most warehouses. Not suitable for your intended use. So unless you want to custom order some forgings. $700.00+ your other option is using Keith Black hypers. Also usually not stocked by warehouses.
I am going thru a situation with a customer right now.
He is on a modest budget and insists on using a 402 block and crank. Plus his buddies keep advising him on this build.
He had a good 454 short block but traded it for some reason. Now he has to pay the small bore BBC penalty.
Here is what he has to work with.
402+030 2-bolt block.
oval port 112 cc heads.
Problem 1= because of cost and availability, he had to go with replacement pistons, universal dome, .020 short.
Problem 2- I advisd him to at least install aftermkt valves and hard exh seats in heads and 2.19" intakes. His buddies say no. Not needed on small engine.. So it's basic work plus trying to find usable springs/retainers/seals for the cam he insists on. A .700" lift 108 cl. Roller.
Problem 3= Valve to piston clearance with stock design piston. Glad I'm not assembling this engine.
I could go on for a couple of pages but engine people will see what this is going to turn out as..
Just let your "expert" buddies help you with your engine. The guy with 40 + years at the machine shop don't know crap!