what is the WMS to WMS measurement on a 78-79 Ford 9"?

depends on what you pull it from... F150's are right around 65". EB's are around 58"' Don't know about the ones out of cars

F150 and Full size Bronco's 4x4's are wider than 2wd. About 69".

i need it to be atleaste 65" or so. that is what my 8.8 is, which i will be replacing, and i dont want a dignificant difference between the two....

Just get a 60. There are a lot of them out there out of older F250's that are 65". The one in my Bronco started that way and the one in a stock one owner 68 2 wd F250 I have is 65. You know you want a 60, you know you need a 60, just do it.:D