I just pulled those pics off the internet. Even though you said "old style", I was more concerned whether or not you knew that there were 2 sizes to choose from.
Are the parts not compatible, or is it a period-build type of thing? I know they were made for several years, with various improvements for each iteration, but I had assumed that all 3 San An frame parts (the Main "tube", the swing-arm, and a large or small seat sub-frame) were structurally compatible throught the various iterations. I'm an enthusast, but I'm (obviously) far from being an expert. Mad props to all the experts out there.