Does a LS swap into 1968 Chevy C10 require major modifications?

[HeavyHauler]

My truck is a original 1968 Chevy C10 SWB 396 bigblock truck and I have the original engine but it needs to be entirely rebuilt.

I have a couple of all aluminum LS1 engines and a 5.3LS truck engine and I am thinking about putting one of those in temporarily until I can get my bigblock built the way i want it.

I dont want to cut on the truck at all or weld anything to it that alters the originality.

Can the LS engines and overdrives tranmissions just bolt in without any welding or cutting on the truck or chassis provided that you have the correct engine mounts and transmission mounts?