2wd to 4wd conversion, how hard is it?

[Joseph2001]

Ive been needing a frame for my 72 gmc k25 and have been holding back as long as I can on buying a 73-87 frame to use, they are super cheap where I am. There is a 71-72 chevy 2wd here in town that is much better shape and than my gmc and I was wondering how hard it would be to convert it to 4wd using the 4wd stuff from my gmc?

My thinking behind this was I can drop my 4wd stuff under the chevy and be ready to go. Then my dad could have my gmc cab to build his.