I don't know all the details, but can give you some of the differences you need to be aware of. For instance Chevrolet never made a long wheelbase 1/2-ton while GMC did.
This is all assuming you have a 1/2-ton short wheelbase truck. If its anything else the details might be a little different.
The front crossmember is different between Chevrolet and GMC. If you use a Chevy frame you'll need to deal with that, probably by swapping the crossmember.
There are two differences between the '47 - '53 frames and the '54-'55 1st frames. The bellhousing crossmember is different, the later frame has an angled pad for the bellhousing mount where the early frame has a flat mount. If you want to use the '51 bellhousing this could be an issue.
The second difference is that the kickup over the rear axle is lower on the later frames. Probably not a problem using a later frame under an earlier bed, but would be a problem the other way around.
Also some trucks have a crossmember under the rear of the transmission. I've never seen it personally, but I believe it only occurs on the pre-'54 frames. I know its not on any of the '54-'55 1st frames I have and the '53 GMC currently in my shop doesn't have it either, though its not original in other aspects.
Two other frame related differences I know of are the two different types of shock mounts and the two different rear cab mounts. I can't tell you the years affected from memory.
And one more thing to think about. The frame is the same under a panel/Suburban as under a pickup. But the panel/Suburban will have some mounts you aren't going to find on the pickup. Both frame types will have all the holes for either application.
So that is a quick rundown on the differences as I remember them. I hope this helps.
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I completely missed that you are in Victoria. Cletis is right that Canadian GMC trucks had Chevy motors and I would presume that front crossmember would be the Chevy type. Is your truck US made or Canadian made? Or are you in some other Victoria?
