Need help on a new purchase

[Coleman]

Here's my ultimate goal, I want a (67-72) 4x4 that will be able to handle the occasional off road and the ablility to get there at reasonable speeds on the highway. Add in disk breaks, PS and possibly air conditioning as a bonus.
I currently have a 68 K20, SM465, Rockwell 221T. The SM465 is starting to go out, getting tight and tough to shift. I've run across a 72 K20, cheyenne super? with a 350/TH350 and np205 with PS, PB, air for 1000$. It runs but the TH350 is junk. It needs the usual rockers and one cab corner. Looks like someone puttied up the rain gutter over the windsheild but I can't really tell. It has the utility box instead of the regular long bed but I can swap that out. I can do all kinds of combinations between the two trucks to make up one decent truck except the tranny. I would really like an overdrive so I can get decent speeds on the hwy. I guess the question is, should I wait and find an 80's K20 to get my front disks and 700r4 for the 68, or do this 700r4 conversion on the 72 which has everything else, or just put in a rebuilt TH350 back in the 72 and put up with the high rpms on the hwy. My guess is the sm465 (4 speed granny) and the TH350 are going to be the same hwy rpms (sorry, haven't had time for pics)