It should make things worse. Not impossible, but you are going to need some detailed schematics( of original truck, of donor engine, of donor dash) and basic electrical knowledge of relays, switches, fuse blocks, etc. I have the GM electrical manual of my 91 truck, so i have 1/3 of the diagrams i NEED. I am at the beginning stage of what you're describing, 98 dash in 91 Silverado with 5.3 and T-56. Stay tuned, i will open a thread when i have all the parts and begin the fun!
1991 Silverado ECLB
LM7-T56