Have you looked at the Ranger Torque Splitter from Advance Adapters? It goes in front of your SM465 and moves the shifter back 7 inches. It sould be the easiest way for you to get overdrive and then be able to split gears on the hills. Less than $1500 and you'll only have to shorten a drive shaft and cut two holes in the floor.
I understand your siutation completely, I owned a boat rental business and there was lots of time spent teaching the employees how to handle our "delivery" truck which was a manual trans 4x4.
With your transmission in granny low and your transfer case in 4 low, you should just be able to creep out of the ramp. Literally just take your foot off the clutch with greater than a 50:1 crawl ratio.
I hate to say it, but you might be better off selling your truck and buying one with everything you require already in it, cause the conversion just won't be cheap.
