Classic/Antique Car Repair: TRANSMISSIONS, steep inclines, model chevy

Question
Howdy Roger. I have been muscle car and street rod all the way but I am planning on building a sixties model chevy p/u truck. maybe one of the first model fleetsides.(maybe). I plan on using a 250 six cyl. with clutch. I would like to use a tranny with a crawl gear for steep inclines with an average load in the bed and an overdrive for max gas mileage. Are there any trans. that will work for this? Or will an overdrive trans with a low rear gear be better? ( 4 or 5 speed )  

Answer
I'am not that much into the truck line but I have a 2000 chevy silversdo and if I were you I would go with the (5) five speed tranny as it will be less work and I think that with the extra gear and the low first you will be just fine, but if I were you I would put a nice 327 / fuely  
under your hood with a 4.11 rear and a 4 speed and make it all stock looking than you will have something, but the way you want to do it is also cool. so i say go for the 5 speed.
good luck
Bigw45 / Roger