After bringing home my new acquisition/project a week ago, I've had time to appraise the overall condition of the bike. Concern one was the seized engine.
I've seen a lot of ratings on the internet about the effectiveness of different brands of penetrating oils with a homespun recipe supposedly topping the effectiveness scale by a long shot.
A 50/50 mix of acetone and ATF (Automatic Transmission Fluid) is the suggestion and in my decidedly unscientific test, after flooding the cylinder, the piston freed up within 36 hours of application. This is good news.
Next up, how good are the crank bearings. In my Bultaco experience, more often than not the big end bearing is shot and a connecting rod will be required. We'll see.