81 lwb to swb and tbi coversions question

[eke82]

i have a 81 lwb 4x4 i want to shorten it to swb. I know there has been posts in the past but i am not computer smart enough to find the posts after looking for an hour.
also i have a 89 suburban donor that i want to install the tbi and radiator support with newer style lights in the pickup . Do i need to install the complete harness out of the surburban or can i just install pieces. the pickup originally had the electronic spark managment
thanks eric everingham