Hey Man,
I have an M-20 in mine and it has a Hurst Competition Plus on it,
the trans/shifter combo came out of a 66 Malibu so I assume that's the original application,the biggest problem is it wouldn't come out of the floor the same place as the 81 shifter,mine was v-6/3spd,but I imagine that's the same as the 4spd Saggy,I cut my shifter hump loose from the floor and moved it back like 3 or 3 1/2 inches,it did clear the bench seat with it all the way back but not by much but as I've put buckets in I wasn't much concerned about it,although the Comp Plus works good I've been playing around with the idea of a Hurst Super Shifter as I've always wanted one,probably have to move the hump again if I do but well you know,I don't think you'll find a shifter that'll work with the G-body factory location as the Saggy's reverse lever is on the trans cover
and they mounted the shifter on the tailhousing mounting bolts where the reverse lever on the Muncie is on the tailhousing so the shifter has to be behind it,I think you could probably mount the stock shifter to a Muncie as they're similar size but you'd have to come up with a really funky reverse linkage to mate to the Muncie reverse lever and of course modify the 1st thru 4th linkages to fit but then you'd have to come up with a really funky reverse linkage to mate to the Muncie's reverse lever,I won't say it can't be done but well you know where there's a will there's a way! As for me the moving the hump made better sense,
hope this helps! Later,KillerDave