Vortec heads on earlier 350.

[L31MaxExpress]

Get them as bare castings, I made the mistake of buying them loaded. Loaded with cheap **** Chinese parts. The castings themselves are Aussie or New Zealand made and are fine.
Stock applications will react like popping an actual vortec head on 30-40hp and similar tq numbers. Benefit is you don’t need a funky intake or adapters to work.

I never saw close to that on a mild combination. TBI to Vortec head swap gained 15 hp peak to peak and about 20 hp at redline. The Vortecs lost torque. With OEM exhaust manifolds it would have even made less of a difference. The mildly cammed TBI headed 355 I built made 320 hp and over 400 ft/lbs at the crank. 10.4:1 compression on 87 octane using 26° total timing.