Hey James, That trans if it was a 73 IRS it cant be converted to swing as a 73 and later only has one side cover, so..... That beaing said we need to know is it a 437,412 or 3;88 ring & Pinion. Where did the trans come from? Do you know who built it?
Your best bet would be to take a 73 and later guts with the 9 tooth first install that into a 71-72 trans with a 4;12 r&P go with a 1;48 3rd and a 121 fourth or maybe a 112 4th depending on the amount of Hwy driving you will do. Then add your short axles (keep in mind you will want a super diff, poor mans posi, chromolly nut retainer and maybe some good axles) There is a full tilt trans for sale aprox $1800 with all this in it.
If you want more on it drop us a line.