I am in the market for a 70's Ford pickup. I would like one that is a 4x4 with a straight 6 and a 4 speed manual transmission. I'm wondering if this even exists. I've been searching and it seems that all the 4x4's are V8's.

 

early 7Deez F100 4x4 was commonly built with the 300-six, 4 speed (NP 435) and a single speed T/C (D21).

 

yes they were. unfortunately almost all have been converted to V'8 engines over the years by the "i have to get there yesterday" types.
two of my snow plow mules are 1979 F-350's with 300 6 cylinder np435 transmission and 205 transfer case.
real work horses.

 

Good to know. I was thinking about just getting a V8 4x4 and swapping the engine. Is there a good place to go to get a straight 6 without having to buy a whole other truck to pull one out of?

 

You could find that buying a truck gives you parts you may need like the frame towers, various engine brackets, a radiator, etc.
Just depends on what you find parts wise.