[dsraven]

i'm with mr48. lots of money tied up in adapters etc. why not use the overdrive unit if you're gonna spend the bucks. then you get better low end and can still go highway speeds without overclocking the old 6.
would you use a new trans cross member and mount along with the existing front engine mounts and rear engine mounts? if so there would be a good reason to replace the old mounts so all are fresh and flex about the same amount, hopefully. otherwise there are 3 mounts in a row and that can cause some issues with stress if they have different ratios of compression. like a kids see saw effect, if one end gets loaded up it can pivot on the middle and cause the other end to unload or whatever. just something to think about.

what about a complete new drive train. if you want to stay with a 6 how about, say, a 4.2l inline 6 from an envoy/trailblazer with an overdrive trans already connected or a 4.8-5.3 from a pick up. they would have fuel injection and an overdrive trans. always start easy, give great mileage and drivability, no foul odors from the exhaust etc etc. it would be some work but if the truck is in good shape it would make it a lot more fun to drive. buy a write off donor vehicle and you should have all the stuff you need.

your truck and your pocket book. do what you want and have cash for to get the job done in a timely manner. otherwise it may be on the back burner longer than you think. thats how projects end up on the for sale list.
do a feasibility study first so you know the totals before you start. for the auto swap this is at least a partial list, maybe not complete.

-adapter plate and flex plate kit
-transmission and torque converter
-trans filter and pan gasket kit
-trans torque converter seal
-trans output seal
-fasteners to mount flex plate to engine, trans to engine, cross member to frame, trans mount to trans, etc
-rear trans cross member
-rear trans mount
-trans cooler lines, fittings and retaining clamps
-trans cooler hoses (to allow for flex near cooler connection)
-hose clamps etc
-trans cooler and mounting hardware
-trans fluid
-custom fit drive shaft for length and to fit rear axle yoke. include the yoke to fit trans
-automatic floor shifter to match trans, floor boot and linkage or steering column swap for one with auto shifter to match trans, with shift linkage and related wiring
-wiring, fuse and switches etc for park interlock (to allow starter to only work in park/neutral) and back up lights
-remove old clutch pedal assy and linkages
-plug for hole in floor where clutch pedal used to be