You have a number of good options. Start with the idea that a '65 B18D is rated at 90 HP in good shape, and work up from there:

Change the exhaust manifold to the later one with dual headpipes, and you've got 95 HP. This can be from a '67 car (some '66 may have had it too) with the integrated intake portion, a '68- carbureted car with the intake cut away (you then retain your current intake -- the integral intake on the '68 type is garbage), or an injected car. No point doing anything further without improving the exhaust manifold, so plan on that at least.

Shave the head down to 3.685" thickness, and you have a B18B rated at 115 HP with the improved exhaust manifold. You would have to use premium gas.

Use a D cam instead of the stock C, and you have something more than 115 HP, with a midrange torque improvement as well.

OR:

Start over with a B20B, the carbureted model. The intake ports on the B20 injection heads are larger than you really want for a street-driven car. A stock rebuild on that is rated at 118 HP, and you should be able to use mid-grade gas.

Build that with D cam instead of a C, and you have something more than 118 HP, with improved midrange torque.

I wouldn't automatically discard the idea of building a B18. They are inherently smoother than B20s, rev more freely, and tend to get better fuel economy.