If you don't have a GMC, the prices are pretty good now and lots of them available. We've only had ours for about 18 months and love it and the community.If your into cars or/camping/traveling, and can afford it, go for it IMHO.
The 4l80e is a modern electronic version of the th400 with a 25% overdrive. I was looking for a complete package with low end pull as well as low rev's at cruising speed for the enhanced mileage. The motor can be bolted to the original th425 with a simple adapter but you sacrifice either hi or low speed performance without the additional gearing. Of course doing it the th425 is a much simpler and less expensive way and probably within many peoples ability. And I'm sure will give excellent results. I've never followed the norm, always looking for a better (hopefully) way and not being afraid to give it a try. Maybe off bubble a little , who knows. Anyway, it's the approach I've taken and time will tell if it's right.
I'm running a 215/85/16 tires so the rpm's are slightly off the more popular 225/75/16.

215/75/16 tire; 225/75/16 tire

55 mph 1869 rpm in OD, 2492 in direct 55 mph 1939 rpm in OD 2586 in direct
60 2039 2719 60 2116 2821
65 2209 2946 65 2292 3056
70 2379 3172 70 2468 3291

I'm afraid things are going to slow a bit. We are heading to Las Vegas for SEMA and then on to San Diego to drop off a prop I built for our grand daughters dance studio. We have Thanksgiving and Christmas holidays which fill the calender pretty well too. Then off to Indio for the FMCA rally and over to Quartzsite for probably a month. We may only have a couple of weeks to work on the project left this year.
Have ordered the cv half shafts for the 2012 front end and need to ship the outer cv's out to get axles made now that I have fixed dimensions.
It looks like it'll need a 2 9/16" spacer on the right side to keep both half shafts equal length.
I may start on the wiring harness and try to source a couple of electric connectors over the holidays. The plan is to keep it all electronic, hope I don't regret that direction. I like the potential fuel gains as well as the self diagnostics capabilities of the electronic engines. Time will tell.
Thanks for the interest everyone.
Hal

Hal StClair wrote on Fri, 24 October 2014 13:14

I'm afraid things are going to slow a bit. We are heading to Las Vegas for SEMA and then on to San Diego to drop off a prop I built for our grand daughters dance studio. We have Thanksgiving and Christmas holidays which fill the calender pretty well too. Then off to Indio for the FMCA rally and over to Quartzsite for probably a month. We may only have a couple of weeks to work on the project left this year.
Have ordered the cv half shafts for the 2012 front end and need to ship the outer cv's out to get axles made now that I have fixed dimensions.
It looks like it'll need a 2 9/16" spacer on the right side to keep both half shafts equal length.
I may start on the wiring harness and try to source a couple of electric connectors over the holidays. The plan is to keep it all electronic, hope I don't regret that direction. I like the potential fuel gains as well as the self diagnostics capabilities of the electronic engines. Time will tell.
Thanks for the interest everyone.
Hal

When you were first doing the original layout of this project, did you give any thought to using the whole front frame clip from a 1 ton Chev/GMC 4X4, using the 454 big block, 4L80 transmission/transfer case and only the front driveshaft etc.? I know they used to build the so-called "wedge trucks", that were so popular with auto dealers, by cutting 1 ton 4X4 pickup apart right behind the cab, and using just the "front drive system" for motivation. They then stretched out the "rear frame" to what-ever length they wanted (depending on how many cars they wanted to haul) and used a Olds Toronado rear axle under the back of the frame. This gave them the HD front suspension, the OD transmission and the wiring package for the 454 that most used (with EFI). Just wondering! Your package however is looking good!!