Chev engine identification

[Lang]

This engine is a a replacement hence the R prefix and ratty hand stamped numbers. Up to the 60's replacement engines were supplied blank and the mechanic would stamp the old number but not the prefixes (which told what factory and date). Unfortunately without the letter prefixes of the old number we can not identify it from this. No Chevrolet factory 6 cylinder engine number was ever a single "R" prefix.

Your casting number does not match any I can find. There are many detailed Chevrolet casting number sites listing every model ever made. The year and number are not sequential and much later motors had smaller numbers in many cases.

I believe, if you look hard again at your casting number it will be 383 7 004

not 383 1 004. Which would make it a mid-fifties 261 - a winner out of all the Chevrolet early 6 cylinder motors!