Engines from the factory are rated at the flywheel, never at the wheels. So a stock L20B was 110 HP right from the factory with a single Hitachi carburetor.

To make 150 HP (at the flywheel) you need twin 45s. 40s will not do it without the expensive work previously referred to -- or a turbo!

The Datsun U20 engine (also 2-liter) had a factory 150HP option, which was basically twin 44 mikunis instead of twin hitachi 38s + a higher RPM camshaft. The basic performance difference between U20 and L20B is the cylinder head design, hence the need to choose a good cylinder head.

V91 versus U67 cylinder head. Dunno.

219 and N04 were the SSS heads. Nissan competition sold the U06 as an SSS head. Dunno if those are the ones you want on an L20B, but for L16 & L18 are the good ones.

210 and N21 are the common heads and are OK, but not a great hi-RPM choice.

A good L-series head works just fine when done right. Just do minimal bowl work and port matching (not fully ported) and have to rev it up (cam and springs) to make 150HP. And let it out with 2.5" exhaust. Use 9.5:1 or 10:1 compression.

Oh and it won't work without the right cam. All this work is estimated at $2000-$2500 USA for the L20B.

A stroker 2.3 L20B (L cylinder head, but using Z-series block) makes 150HP -- at the wheels, so higher at the flywheel -- using similar components.

Also note that a stock junkyard KA24DE makes over 150HP flywheel with zero mods.