Transmission on the LS, or keep yours?
Wiring, yes, it was time consuming- I am not familiar with the MSD kit (or, if I helped with one, I did not know it).
I have never helped on an install of an LS series engine, in a classic truck or car, when the front end, steering, power disc brakes, and rear end weren't ALL changed/replaced/new parts.
The ones I helped with pretty much were like taking a frame and a body and making everything fit the engine & driveline. Not that it is a bad thing at all. Folks do it all the time.
Brad