I was out tinkering in the garage again this afternoon. Didn't get too much accomplished. Just separated out boxes of hardware, and started pulling the transmission off the original engine. Noticed a couple other differences between my two engines. The case halves are cast with slight differences.
The clutch assemblies are different.
I found the frame serial number 6178.
The wheels are 19 inch front and 18 rear. I'm thinking now it's probably a Trailblazer. That serial number doesn't seem to fall into the 1958 serial number range, but maybe I'm looking at the wrong numbers.
Interestingly the forks that I have came with a 21 inch wheel, and chromed triple clamps. No idea what those came from yet. I'm giddy as a school boy about this project. Researching and learning all the details is a lot of the fun for me.