64 GMC SWB 2wd to 4wd need advice

[1964GMC]

My street cruiser project has just become a beach cruiser/surf fishing project. What do I need to convert to 4wd? Can I just swap the front crossmember for something in a later model? Or would a frame swap be the best idea? What would fit? Not wanting to go full on monster truck, just 4wd with wide/high floatation tires.

Bad thing is I have a finished 2wd chassis with '84 front crossmember/discs and POR15 frame. 283 is built and coupled to a 700r4. This truck already has rear leaf spring suspension.

Thanks in advance for the advice.