First, welcome to the board. By reading your post, I assume that you want to keep it as close to stock as possible but with the added benefits of "modern technology"

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[email protected] 2x" width="20" height="20" />. You are on the right track right off by starting with the brakes/drive train. If I were going to rebuild one as you are, I would go about it in this fashion:
#1 - Disc Brakes F & R
#2 - Power or Hydroboost brakes
#2 - Power Steering
#3 - EFI/SEFI
#4 - Transmission
I would definatly go with disc on all corners because of the stopping ability. And to do that, I would look at BC Broncos. The front & rear conversions are both using GM calipers and are probably the best on the market for kits. Once you do that, I would go with a hydroboost/power steering. They kind of go hand in hand or just do the PS because without that, you can't run the hydroboost. To get better gas mileage I would find an EFI/SEFI set up off of a late 80's/early 90's 5.0 and cob onto all of the fuel injection equipment. Last is the transmission. You can go with the 4 speed set up, but those are the t-18 or the NP435 trannys and they are truck transmissions and will feel like it. If you go with the ZF-5 speed from Wild Horses, you really can't go wrong. I personally stick to BC or WH when I order my stuff, but that is me. I have dealt with JBG but only if none of the other vendors have what I am looking for. Just personally, so take that for what it is worth.
A question for you, you said you want to go with 3.73 gears...is there a particular reason or just a happy medium? What are your current gear sets at right now? If you post up your VIN # or go to BroncOhio's web site (
http://www.broncohio.com/tech/ebvins.html ) and look at your VIN there to figure out what your gears are. But that is the route I would take to get started.