Hey Tom,,
I would not mess with the 4BT for what you are going to use your truck for, Stick with a 6BT. You will be much happier with the power potential.
Here is a link to my Cummins Conversion:
http://www.oilburners.net/forums/showthread.php?t=21780&highlight=cummins+conversion
As far as power and performance, Here is a quote from the Drag Race Results last summer:
At the 2010 IDI Rally we were able to drag race our trucks thanks to Chris for setting up that event, It was a ton of fun and we were able to see what our trucks with one pass at the dragstrip.
I have been wondering what Big Ed compared to,. so this month's Diesel Power Magazine has a shootout with all of the big 3 Diesel Trucks. They drag raced them empty and towing at the strip and up grades.
Here are the results of the Drag Race:
F350 CC Dually curb weight 8540 Ran a 17.40 at 84 MPH
GMC CC Dually cub weight of 8100 ran a 16.60 at 86 MPH
Ram CC Dually curb wight of 8060 ran a 18.00 at 80 MPH
(Curb Weight is fuel fuel tank and no driver.)
Big Ed with actual race weight of 8240 ran a 16.58 at 81 MPH
These trucks are just under 400HP and and 750 Torque. The Dodge was the least with 350hp and 650 Torque.
So I think its pretty cool that my ole rig will run with the Big Dogs that cost $60K and up.
Keep in mind that my truck is not what I would call Bombed. It has bigger injectors, fuel pin, 3200 RPM Gov Spring, Bigger intake snail, Propane, and free flowing intake and exhaust. Nothing radical, no twins, huge injectors, fire ringed head, and doesnt belch out bunch of smoke, just enough. All of my numbers (boost, pyro, water temp, tranny temp etc) continually run in the safe numbers. I feel that it is just a good solid performer, and the Cummins isnt breaking a sweat!
Sorry I cant elaborate any more about the 24V wiring and computer but the 12V is a way easier swap!
Good luck with your decision and let me know if I can help.