Member here BPE sell them. Have one in my R3 W9 deal.

This is my opinion so take it as you want.
Build an G3 Not an R3. The stock heads are more than enough to support what YOUR looking for now and the blocks are as tough as the R3 and you can get them anywhere. CNC the heads down the road and NO Victor small block head will touch it.
The thing with the G3 is that there is TONS of parts. Break something and Your not hunting for Hens teeth.
Once again Just my opinion.
If your going with the R3 and using indy heads or W2 I have new in the box TD rockers shaft mounted 1.65 ratio.
Matt