There are a couple non-stepped couplers available - but make sure the part is applicable to the 71-72 TH350/NP205 combo - might have to call before ordering online.
Some later applications have a different length coupler.
For instance - tech info on this one says it specifically will NOT work with 72 and earlier, incorrect length (4+1/8")"
https://torqueking.com/product/30001...pline-coupler/
So that is what you want to avode.
These might work, but not sure, length is not listed:
https://www.summitracing.com/parts/a...4aAnDdEALw_wcB
https://www.ebay.com/itm/Chevy-GMC-T...-/282603673976
https://www.ebay.com/p/NP-205-Np205-...pler/675688490