If you don't know what your wheel bolt pattern is --- here's a link to a webpage showing how to measure that.
http://adaptitusa.com/index.asp?PageAction=Custom&ID=4
Might be just as easy and "cheap" to buy some wheel adaptors -- they'd already be drilled and ready to go -- then you'd just have to weld 'em up to
the jackstands.
You can't weld to cast iron - unless you're good - and then it needs to be preheated etc --- so if you are shopping for jackstands -- do yourself a favor and get SIX TON versions (they are taller - allowing better work height) - and get them with steel or cast steel (not iron) saddles.