I think they are a variant of the "LA" class

In Reply to: Engine-type designation question posted by Doc Hogan (dochogan) on April 30, 1999 at 09:37:11

IIRC a "B" is e.g. 383, and an "RB" ("raised B") is e.g. 440. "A" was the original 318.

But I'm not a gearhead.

...tom

Yes, I thought so as well, but still a variant. Check link inside. (Matt D) 16:18:08 4/30/99 (0)