As Cletis says, the 228 will exchange with a 248 270 and the 302. You can bolt up your bell housing and transmission to the later engines too. You will have to change the timing cover back plate in order to have a front motor mount as stock. This will mean that you will have to drop the pan, remove the flywheel and remove the cam in order to replace the timing back plate.
Finding a 228 248 270 or 302 GMC engine is going to be difficult to find in Canada, I think they did not use the GMC engines in the GMC trucks, they used Chevrolet 216 235 and I am not sure about the 261 (Those were also used in the canadian Pontiac's). You will probably have to have an engine shipped from the states.
I am doing the swap also. I have a 1959 302 that I am putting in my 48 GMC Suburban. If you want to keep the six volt, you may have a problem. Finding the correct 6 bolt/6 volt 139 tooth flywheel is pretty difficult to find. The 228 flywheel is four bolts. The newer 248 270 and 302 engines have a 6 bolt flywheel and it has 174 teeth?
