In the context of what the OP is looking to do, I don’t look at it that way.

My experience has been, at least when it comes to factory BB and SB heads, there is no “magic” valve job that miraculously yields significant increases is flow.

However........ there are certain ways of doing things, and practices that I’ve seen implemented that end up reducing the flow of your stock heads........ and sometimes by a fair amount.

So, the “trick” VJ is primarily one that doesn’t make your heads worse than they were....... and maybe boosts the area under the curve a bit.

For this type of build it’s best to start with castings that haven’t already previously been subjected to some flow diminishing work(its often not possible to get back what was already lost......... without doing some “other than” valve job type work).