Thunderjet Custom Deluxe

I found a 50's Thunderjet Custom Deluxe bicycle in an old building on our farm. I immediately thought a swinger front end and a motor. Only thing I am worried about it being a woman's style bike with no crossbar on the top, but it has 2 down tubes. Would I have to run a cross brace across the top?
This is the only picture I can get until I dig it out.

I don't think they're to rare, but I really have no clue. I'd hate to chop up a rare find though, I made that mistake with a 1940 Willys Sedan Deluxe when I was younger and still kick my butt everyday for it. I think I could make it so if need be I could return it to original. I'm really liking the look of the step through's though. Decisions Decisions.