The 350 was the first B engine. It was followed by the 361, 383 and 400, all dimensionally the same except for bore size.

I believe the 413 was the first RB. The RB383 was a stopgap engine, couldn't keep up with demand on the B engine IIRC. But as much as it gets mentioned here, they are really few and far between. So 413, 383RB, 426, 440 in that order.

DO buy the whole car, for cheap. That engine stamping is indicative of something that may be valuable, may be just an oddity.

But thanks for bringing it to our attention.

If you were REALLY lucky, the cylinder heads wouldn't have soft plugs on the ends.

And whoever would confuse that engine with a Poly needs to go to Remedial Mopar Engine Identification class.

R.