Before you consider using any other frame, consider the amount of work it will entail to mount body 'A' on chassis 'B'. Of course it will fit, but all you will be using of the original car are the outer body panels as every thing else will need to be majorly modified, cut out and replaced or ...... whatever.

That original frame is very strong as long as there is no, or at least minimal rust. It's what can best be described as a 'top-hat' style frame. It is made up of a bottom plate, then has an inverted 'U' riveted to it - many rivets. This will in turn give it a boxed frame strength. Here is about the best source of parts I know of to modernize that frame: http://www.chassisengineeringinc.com/ . Kind of a strange search tool on their catalog page, but once you figure it out, works fine, I spent quite a bit of time last year looking at their bolt together frame components and was impressed at the fit and finish though I might weld parts of it solid once I was happy with the final assembly.

The other source mentioned above is Fatman: ..::FatmanFabrications::... Their on-line catalog is a .pdf and is very slow loading. More work, but good products. Not sure I would want to consider others with that top-hat frame