As for using a B18 carb setup on a B21, I am thinking probably not. If I am correct, the intake and exhaust port spacing was changed between these 2 different series of engines. The B18 has the ports spaced like a small block Chevy motor. Looking at the sequence of the intake and exhaust ports, starting from the front of the engine, is EIIEEIIE. On the B21 the port sequence is IEIEIEIE. The B18 manifold for the SU's is not going to match up to the B21 head. You might need to find a Canadian carbureted B21 intake to put the carbs on your B21.

Myself, I am in the process of getting ready to switch from the K-Jetronic mechanical fuel injection setup to a MegaSquirt-controlled EFI system using a lot of B23 intake system parts.

billy242
1980 242DL/B21F