Frame Swap or Keep Original

[MGF2011]

I have a 49 GMC that still has original frame. It is completely apart now. Question now is do I keep the original frame or switch it out for the newer ride. Im not going to bag it, I would like it to be lowered 3 to 4 inches. just asking for input on the best route to go without spending the 7 grand for a fat man chasis. If kept original can it be lowered and upgraded to get a descent ride? This is going to be a long term project. already have the 350engine for it and plan to keep everthing else as original as possible.