hello, I'm trying to figure out the right combo for a 350/4spd w/ granny low/ and driver side dump tcase.. can anyone help me out? Thanks.

well you pretty much said it your self. go 350/SM465/ford NP205. or if you want something with lots of torque go with a 383 stroker. you could probably find an older ford truck with a 4spd and a 205. but it would be a NP 435 not a SM 465. the ratios in a 435 are
1st 6.69
2nd 3.34
3rd 1.79
4th 1.00
rev. 8.26

465

1st 6.55
2nd 3.58
3rd 1.57
4th 1.00
rev. purdy low (couldnt find it)

what exactly do you plan on doing with this truck?

In an SM465 1st and Rev have the same ratio.
Rev is 6.55:1