Re: frame help?
The old Schwinn Stingray frames (and even some of the period copy-cats) are pretty solid steel beasts. To be frank, I'd worry less about the frame and more about whatever wheels you use. Especially with the HP you're considering. Mounting such an engine in this kind of frame can be loads of fun too, I've heard. That said, I confess to being curious to see the end result though.
"There is nothing wrong with wanting a motorbike that is an extension of your personal taste and fashion sense; if you must ride somewhere, I say do it with style