The TBI heads are way down the list as far as the bottle neck goes in power. I have made 330 hp with a set of stock heads. I ran a 12520270 Goodwrench L05 years ago. The 8.75:1 compression version rated at 180 hp and 300 tq. With some basic airflow modification and tuning it made 204 whp and 306 wtq. Small 203/210 @ 0.050 GM roller cam bumped it to 250 whp and 320 wtq.
When I bolted that engine in, I put tri-y headers on that I swapped over from the 305 that was in it. I kept the 2.5" GM true duals that were already installed on my 83 G-van, but had previously added a Dr Gas X-pipe to them. Basically cut the pipes behind the trans crossmember, welded the X-pipe to them, then had a local exhaust shop bend up pipes to connect the Thorleys to the X-pipe, leaving the OE mufflers. When I first ran the thing it had an OEM TBI manifold and 350 throttle body. That manifold developed a coolant passageway leak from its previous life and neglect. I bought a 3704 and had it bored to 2". Put a 1" tall open oval center 454 spacer on it with a 2" bore 350 Marine TB and a 454 air cleaner and duct. The 454 aircleaner had a built in power bowl. Then I put 1.6 full roller rockers on it. When I first put the engine in it made 177 whp and 262 wtq with the headers, older OE dual exhaust and X-pipe. After the manifold/TBI/air cleaner swap and 1.6 rockers it made 204 whp and 306 wtq. Then I swapped a 1996 LT4 roller camshaft into it. Cam swap pushed it to 250 whp and 320 wtq.
Also for reference a stone stock light duty 210 hp crank rated L05 350 TBI does not make 160 whp.