[big10]

I believe all 383 road runner engines were rbs. They had 440 heads ,intakes and exhaust manifolds on them. Please correct me if I'm wrong.

While a 68 GTX and 68 Roadrunner both had "906" heads, the 383 is still a B block and the 440 is a RB block.
The intake manifolds don't interchange between B and RB.
383/440 exhaust manifolds are probably the same casting but the 69 1/2 thru 71 440+6 exhaust manifolds were different than the 4bbl engines.