I've ran a 400 in my combo for some time. If built with the right parts it will work well and pretty reasonably priced. You'd have to run a manual valve body and the gv is not necessary but would be a plus. I know for 12 bolt passenger cars Gm made a 2.56 gear, which is what I ran with the 400 non gv for some time. Worked well for everyday driving. If you Trans brake it you wil have issues with the rear gear. I switched to a 3.08 gear and 3 series carrier when I went with the gv. Better mileage than the 2.56 but same end result with the Trans brake. As long as you just foot brake it it will last. Pm me if you want the details on how to build the tranny or I can build it for you with the right parts.