engine swap

[1983shorty]

hey all , i am going to upgrade my 83 gmc 2 wd 1/2 ton shortbed from the straight six to a 350. getting a 81 monte carlo with a recently rebuilt 350 and 700r4 tranny. should be a pretty easy swap but i want to be on top of all the things i need to change before i start. i will be getting a new radiator regardless so thats no problem . probably will run headers so exhaust is pretty straightforward. i assume i will have to relocate the crossmember for the trans and possibly change the driveshaft length. currently have 350 trans. will i need new frame mounts for the 350 engine or will i be able to use the ones the six uses ? what about the wiring harness ? really looking forward to this ! its a southern truck with 73,000 original miles and aside from a hole in one cab corner is VERY solid.