I hate "ratings"......its BS.....150hp is not what a stock 318 Longblock is capable of....its how it came STOCK....2bbl, smog pump, single exhaust system through a catalytic convertor.
I would OPINIONate, that a UNCORKED OE 318 Longblock with a double roller timing chain, Aluminum dual plane intake, a edelbrock 1406 600cfm carb, some headers and a Distributor Recurved.....would boost up the power from 150....to 275ish hp....without so much as a cam swap....stock cam.
LA 318's are screamers.....they just need a good Carb, Intake, Headers, and supporting mods....compression is overrated, unless your RACIN'
I wouldnt go MAGNUM 318 unless there were NO LA v-8 engines to be found anywhere......then I would do it, only reluctantly.
There are benefits to each Longblock.....but Magnums are a crapshoot.
Good luck