His '67 B18 should already have a separate exhaust manifold... so the stock one can be used. Or, find a dual downpipe from the FI B20 for a little more power.

One thing to keep in mind... sometimes the thickness of the weber manifold is different wehre the thick warshers go... you have to either grind warshers to suit, or grind manifolds to same thickness. Them warshers have to sit flat or you'll probably have vacuum leaks...

And... don't expect a great power gain with the new carb. But once you get it set up right, you'll like the smoothness and the fact you won't have to tinker as often.... But keep your old SUs around in case you decide to switch back someday!

Good luck!
-Matt