Peter -
It sounds like are trucks are close. Mine is a 95 FLD120 with Cummins M11 Eaton 10 speed OT and 3.91 rear end.
So how much??????
I initially looked into the HT 740 and without a core my first quote was around $6,000 plus install. Since this would only get me to about 55 mph with present rear end I stopped there.
I have since found a few companies selling HT 740's, but don't recall if they had been rebuild. I think I saw somewhere that Allison was rebuilding them as well.
Any additional info would be appreciated.
Bill
2003 28' Show Hauler Motorhome on a 1995 FL 120
www.showhauler.com