Ah, R07 may be different critter,(different bore centers and raised cam etc) but SB2 block is dimensionally identical to standard SBC (AFAIK-certainly some engine builder can chime in here and say I am full of it) except for the lifter bore angles and in fact, many engines are built with SB2 heads with the standard lifter bores. Far as I know, lifter bore locations is not regulated, only other features of the block as described in the rule book (cam position (so a raised cam block would not be legal in production) bore centers, intake manifold pattern, head bolt pattern, bellhousing bolt pattern etc.) I still submit is a legal swap and in any case, the book says engine swap is legal in GT so doesn't matter anyway if the block is different. It is made by GM/Chevrolet. For sure, you cannot identify an SB2 block from the outside. Depending on year, been a while for instance since we saw a big block in a Vette. Same a Gen 1-2 SBC compared to current Gen 3. It would be a legal swap and can run GT rather than MS. Back to DW on Monday.