Well Damn, you already got the 60-E ECM, you're over half way there already. I really doubt you'd have that big of problem with the Tcase. You're a NP208 or NP241 right??? Then it's round pattern and should be the same adapter as a GMT400 3/4 ton adapter I'd think.
Not positive. It's the 4L80-E/NP205 Passenger side drop that is so elusive. The round pattern shouldn't be all that hard. Big difference being, Squares are PS drop, GMT400 is DS drop. Otherwise should still clock and bolt right up I'd think.
You know once you got it done, that trans would probably last 150,000 miles. The biggest problem I hear of 4L80-E's is them going into Limp Mode, which is 2nd gear only to get you off the road. And usually the problem is a sensor of some sort, VSS, TPS or some crap like that and it throws the trans into Limp mode.