if it's something as serious as a bottom end bearing then driving for as long as you can would mean parking it right now and not even starting it..... problem with something majorly internal like this is there will be rogue bit of metal floating about doing serious damage....
It can block up the oil filter and thus the bypass valve will open up and the oil will no longer be filtered so every part of the engine will be damaged, including the "good" cam.
Oil is splashed around in the engine anyway and metal fragments will end up everywhere anyways.... ruining any serviceable parts, you'll have a worthless lump of scrap metal....
Easiest option is to just get another good engine, pull the cam out of the dying engine, pull the intake manifold and timing cover off the replacement engine, swap the bits over, replacing the intake manifold gaskets is generally a good idea on these engines as it's a common problem for them to deteriorate and leak, while you're at it put a new sump gasket on and you should have a good leak free second hand engine......
VN & VP engines are the same so it doesn't matter what it came out of (the only different one was the first of the VN's and it's basically the same anyways)
If looking to replace the engine I'd suggest finding a VR v6, they have a higher compression ratio than the earlier buick's that will suit lpg better.
The previous posts giving you advice are all good suggestions as well.