I have a long bed GMC pick up. It had a diesel then a 350 sbo, and now a 403.

403 info:

KB 403 pistons
Comp. Cams 468/468 218*/218* duration @.50 lift cam
Rochester Q-jet of unknown lineage
HEI with light springs

It has a TH400 tranny with the stock converter.

I am planning to continue running 235/75-15 tires.

I will use the truck for hauling an assundry of goods/feed/hay/manure and towing of boats and other trailers. Also will use it as a way to get back and forth to work....which is a commute of almost 20 miles of 70+mph highway.

All that for this question:

What gear would YOU choose for this truck? I am running 2.73s now. Its ok, but I have yet to try towing with it.

 

Having a Suburban that had 3:73's that blew, and could only find a 2:73 [?] drum to drum - I completely know your situation, in reverse! But I have a 700r4 trans.
If it were me, I'd go with a 3:42, or 3:73 if your towing weight is high.
A 700r4 trans will bolt-up, with an adapter, but make sure it has a shift kit, for towing -'73-'74 GM truck trans doesn't need a switch for O.D. - was all solenoids, only need 12 volts! [had one]
Gets you the best of both worlds - off the line 'grunt', and decent highway RPM's!
3:42 X .70 = 2:39 final
3:73 X .70 = 2:59 final

 

I was thinking of 3.42s even w/o the OD transmission. With a 29" tire 70mph gives me an engine rpm of ~ 2775. Figure a little higher with converter slippage and its still not too bad.

3.73s put my over 3000rpm on my commute to work. Don't know if its just me or if the small difference in rpm would make any difference at all.

I suppose I could always use a larger tire.

I plan on keeping the TH400 for now at least. If I had a 700r4 I would throw 4.11s in the rear end and be done with it.

sb

 

I think you'll find 'recycled' rears will save a lot of time and money!
At the time, noone had a 3:73 posi that I needed, but since "Cars for Kids", there's a ton out there!