On top of the rebuild and I gather you are looking at a non pollution setup?

A. For 150hp atw boost will cost you a 3rd of NA.
B. For 150hp ate boost will cost about 1/2 of NA.

150hp atw

For boost youll need a good T28-T30 with SU Suck through setup with custom manifolds
price 2K plus tuning

For NA youll need 8-10k inc. tuning
For NA option 2 Mild ported KA24e head with prepped rods, forged custom pistons and American GT racing class billet camshaft (only one needed) or Jim Wolf billet. Tuned length exhaust and extrude honed manifold with bigger throttle body or quad throttle bodied setup.

150hp ate
For Boost same as "A" just run less boost or supercharge it instead

For NA mostly same as above with maybe a saving of 20-30% due to less extreme work
For NA option 2 SR20DE with better exhaust or no pollution KA20e head conversion with high comp pistons and Jim wolf GT class camshaft)

Although the L20b block is taller for better rod stroke ratio you best use an L18 block with l20b crank will give you 20mm more bonnet clearance and instead use longer rods and shorter pistons off the shelf, no need for aftermarket.

Ka24e head gives you another 12-15mm bonnet clearance but will need custom pistons to get the 3 valve hemi like head to have enough squish. You just have to look at what American Nissan racers are achieving with the ka24e engines, quite amazing output.