Have you taken any measurements for trackwidth and spring mounts, driveshaft, etc. Sounds interesting if not challenging an IRS Mav would be cool.
How about a early 90's T-Bird rear? .....Unless you just happen to have a 280 Z rear - they are gettting a kind of hard to find. Lots of T-birds around...cheap. T-bird rears are a little wide - but could be narrowed. With lots of measuring and fabrication - just about anything can be done. If you are up to the job - do some searching into the street rod crowd like hotrodders.com. Cleaver
I saw in a magazine where someone makes a kit to put an 8.8 T-Bird IRS in an early Mustang. A Maverick shouldn't be much different.