What size engine for the online/Youtube EC?

I think this is pretty cool but I have a couple of questions.

What if I don’t want to run a 3.58 stroke? Am I married to that or can I use LESS stroke? What if I don’t want that much stroke?

What about if I want to use a 340 block?

How about a displacement limit? Say 380 inches. That gives a builder some room to get what he wants for geometry.

I’m assuming production means iron. Why not pick a head like the Speed Master because it’s cheap? You’d still have the option to use a production head if the builder thinks that’s the best option.
I like the Speed Master Cylinder Head suggestion allot. It is a baseline upgrade option besides magnums, rare W2's (good luck finding afffordable rockers), rare RHS's, and the latest out of production heads: Engine Quests.