As much as people like to say an ohc motor is no good, They do make good useable power and are a more modern engine with less maintenence.

When you say 'more modern', do you mean heavier even with a much less robust aluminium head, stupidly heavy pistons with weaker but heavier con rods, same crank, same bearings, same oil pump innards? Stock B23s are a backwards step, that much is certain.

However to make great power with one you need to port the heck out of the head (doable)

Let's compare stock heads.

B20A, Stock port, 44mm Inlet. Flow@10"H2O

29 CFM @ 0.0875"
54 CFM @ 0.175"
74 CFM @ 0.2625"
88 CFM @ 0.350"
99.5 CFM @ 0.4375"
107.5 CFM @ 0.525"

107.5 CFM is enough for 180 BHP.

Standard B23E, Stock port, 44mm Inlet. Flow@10"H2O

23 CFM @ 0.075"
47.5 CFM @ 0.150"
69.5 CFM @ 0.225"
80 CFM @ 0.300"
85.5 CFM @ 0.375"
86.5 CFM @ 0.450"
86.5 CFM @ 0.525"

86.5 CFM is enough for 145 BHP.

Why is the B23 head's intake flow so bad? It's short side radius is far too small & it isn't cheaply fixable. The only sensible thing to do is bin the head & buy a new 531 head.

The B23E makes a bit more torque than a B20E due to 16% more capacity, but after 4500 rpm it's all over.

Your friends 142 is still nice, but where's the turbo?

BTW, is that radiator really thick or does it only look that way?