Another vote for the 235!!!! If you've got a reasonably decent running 235 I'd keep it. The sm420 isn't slow.....the final ratio is 1:1, like most non-od transmissions....it's just that you don't have a synchronized 1st (Granny) gear so you're basically running a 3 speed. If you're planning on running at highway speeds, the easiest and least expensive conversion is to an S10 .72 T5 transmission. A few simple modifications will let you bolt it up directly (no adaptor plate needed) to the 235 and you'll have a truck that will cruise. Of course, you'll need to upgrade the brakes and make sure your tires, shocks and suspension are in good shape. Even if your 3/4 ton diff R&P numbers are high, the .72 OD will bring down your rpms and make driving your truck a real pleasure.
Just for kicks.....run your numbers through the following RPM calculator and bear in mind the stockish 235 makes it's torque in the 1600-2400 rpm range, with the optimum being between 2000 and 2400. I prefer the lower formula.
http://csgnetwork.com/multirpmcalc.htmlDave
