Some information that I had saved off on Redline serial numbers is if it starts with RA then its an 81, etc.
RA = 81
RB = 82
RC = 83
RD = 84
RE = 85
RF = 86
The early 80s models would be the Proline II and the MXII I believe. The Prolines always had 5" headtubes while the MX-IIs had 4" headtubes.
In 83-84, there was the PL-20, which was basically the same as the Proline II but with different decals.
The picture below is an example of an early 80s Proline II.

If you want to know anything about Redline, contact member osrlracer and he can answer.
- Bob