I just cant see why installing an a833 OD would be cost prohibitive if you had patience and sourced good used parts and disassembled them for a good check out like all used parts should be. Save yourself a bundle of money and fabrication. Just pick up one part at a time and be sure it is a decent quality part by making informed careful purchases. In a year, you will have a nice 4 speed overdrive kit ready to slap in. 300 hp will not need fancy or new parts. Just decent quality and not badly worn. Reman clutch / pressure plate from napa. Napa throw out bearing. Your factory drive shaft will work fine. As long as you dont abuse it hard, it will last years. Your rear end will die fairly quickly if you have a 7.25.
I put an a833 OD (cast iron case from what I remember) in a volare which was originally 318 /2bbl /904 /2.76 7.25. Went 4bbl dbl pumper 650 holley / rpm intake / 360 cleaned up J heads /mild crane cam /headers /a833OD /3.91SG. Every part was used but the lifters , the clutch/pressure plate and generic 2.5" duals dump at rear end. Original drive shaft. It ran very great and fun. I abused the living heck out of that setup and finally broke a couple U-Joints here and there. I mean dumping the clutch constantly at 4K, powershifting at 6200 all the friggin time every day. I was crazy. If you don't abuse a setup made from basic parts you could have a smooth machine for years.
To install a 4 speed hump with no fancy tools: get a new hump for 65 bucks online at one of the 50+ places that sell them (brewer's is good quality from my experience), draw a line on the floor pan around the hump edge, get a jigsaw with a metal blade and some extra new blades and carefully cut 1/2" smaller than the new hump line on the floor board (dont cut thru your crossmember). Sand the floor pan to bare metal 1/2" wide around the opening, sand the hump clean to metal on the bottom contact area. Use steel panel adhesive (follow its procedures) and glue the thing in place. It will take you a few hours and will require no fancy skills, no fancy machinery, only patience. Then the only other mod is the small reinforcement piece to your inner fender for the Z bar pivot and a little hole for the clutch rod.
Guys, is this not good advice here? I mean heck, lots of people have built great hot rod machines out of used parts which were designed to go right into our A bodies.