Thats a nice amp! Judging by the dual drive pots I'm guessing it was based on a Jim Marshall circuit? Its very reminiscent of a Sovtek Mig50. I got my first tube amp from my Dad (he didn't build it). It was a 1974 Ampeg V4 100w behemoth that I added a master volume to and totally rebuilt. It started a lifelong love of vintage amps and instruments. I've been building em and repairing them ever since.
Rusty, you are a man after my own heart. I too love old instruments and amplifiers. But don’t have your skills to restore them. I’d love to see some of your work, but maybe not here as it’s a motorbike forum......shame