Manual transmission swap
OD boxes are probably easier to source and cheaper to buy as they’re not as desirable as the 1:1 box. A 400hp rated diaphragm clutch from McLeod is around $250 bucks plus the cost of a 360 compatible flywheel as they’re externally balanced.. I spent more than some since I replaced stuff with new items like the starter for a later model dodge ram unit..way smaller and cheap. New U joints on the driveshaft at both ends. You’ll need a 30 spline yoke to match the 833 as the yoke for the 904 is 26 spline. Biggest road block you’ll likely run into is that the crank may not be drilled deep enough to accept the input shaft of a 4spd. The easy remedy is to knock off the tip of the input shaft. Some are okay with that method. Others would have the crank drilled which is another can of worms to open. Thankfully I didn’t have to do either with my 68 318.
I also had to clearance the crossmember for the 1-2 shift rod to clear.. just one of many details that I learned along the way