It is directly related to the B18/20 family, it just is about 9 inches longer and has two more cylinders. Most of the internal parts are the same (other than quantity). The heads are different, though, with better designed round exhauist ports, and all the ports are in the same i/e order (unlike the alternating 4 cylinder valve arrangement that puts the intakes together).

It won't fit into a 4 cylinder car easily at all. The 164 it did fit in had an extra 9(ish) inches of wheelbase - all added between the firewall and the front suspension crossmember. You'd have a hard time finding that sort of clearance on a 122. maybe hacking the firewall (and removing the heater and it's intake?) and tunnel to allow the motor to extend 9 inches further back?

Other than the novelty value, just stick a supercharger on the B20 if you want more HP. Or stick a turbo OHC motor in there.
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I'm JohnMc, and I approved this message.