LA Block Bellhousing and Flywheel Options for Test Stand

I've got a few Mopar small blocks that I'm going to rebuild ('69 273, '67 318, '70 340) utilizing an engine run stand that requires a bellhousing and flywheel for setup. Question is; I know there are several different size bellhousing and flywheel combos, does that matter to me? In other words, I'd like to buy one bellhousing and one flywheel that will work on all 3 blocks, for testing only. All three of these motors will eventually be in automatics, so I don't wanna spend a ton of money buying multiple bellhousing and flywheels just for testing purposes. Thoughts?