I have a 700r4 or can trade for a th350. what is the better choice?

I will be running a D300 and my wheelbase is 103

depends.

street use or just trail?

if you need the overdrive then 700r if not then 350.

you are at a wheelbase that it won't matter which.

700r4 has more gears, but are you haulin' ass and crawlin', too? which is more expensive to build or find in the junkyard? things to think about.

run the 700r4 it has a lower first gear then the th350, plus it has overdrive. thats better for crawling and driving on the street. if your going to run it on the street there is a kit to lock up the torque converter when your in overdrive.

700r4 they work great with the 4.3 they have a bad name but not the case rock crawling lower first gear