1971 Duster 360/727

You set your piston height by way of a few simple ways, but to keep it simple, once the piston is on the rod and installed on the crank in the block, the machinist will measure the distance from the top of the piston to the top of the block. Then cut the top of the block.

Other ways are order the piston with a change in where the pin sits or the tops thickness which is not such a good idea in 99.9% of engine building and then there is rod length. The stock rods are 6.123 inches long. You can have this changed. Does can be purchase in 6.125, 6.2, 6.3 or shortened smaller.
Look under "generic rods" for this.
But now where getting in deep instead of Simple.

On the heads, IF this guy that is doing the work an excellent machinist and KNOWS what he is doing, then it might be a good idea IF the heads fit the target goal. And that I don't know. Your target goal is?
I just mentioned several good places to get good rocker arms from.

I currently am running Comp Cams roller Rockers and on the next engine being built (now) is a set Of Hughesengines roller rockers.

The comps I have had for a long long time and everything worked and aligned really well in my Edelbrock heads.