vin # & regi, sell with cab or frame or does it matter??

[cariboo4x4]

On my 1981 gmc 4x4 I am parting out, there's the vin on the dash, and one on the frame. Is there one stamped into the firewall too? I been told they can be on doors and elsewhere. All I can see is the one on the dash. I have yet to look at frame but told its on frame rail by steering box. I have a guy that wants to buy the cab\front clip asap and another guy that wants to buy the frame in the summer\fall. I figure papers should go with cab yet what about guy buying frame? I don't want to create any future hardships for the buyers or myself. Like after cab is in someone else's name, what happens if the guy that bought frame takes it through a mvi? The guy that wants to buy frame bought a 1 ton 4x4 gov. service truck that has an extended frame and he wants to buy my frame so he has the right frame to bolt a box on to. Like what do I tell buyers, etc. so they know what they are doing is good-to-go? Anybody know from experience? I read at icbc you need to get a BC assigned vin if you replace your dash, or if 2 or more vin numbers on a truck don't match.