[Sirrotica]

As long as the base circle on the cam is close to the same as the OEM camshaft you could use the non adjustable OEM nuts. The lift is probably okay with OEM springs.

The way the OP description sounds like the cam timing is off. He's not going to have 15 Lbs of vacuum, or 150-175 Lbs of compression with the valves are off the seat. Just because the cam and timing chain, and gears are new doesn't mean that the keyways are all cut exactly where they should be, or there wasn't some error in the assembly. If the valves weren't seating you'd likely have a miss, or very possibly a backfire when trying to accelerate.

I have had a Comp cam ground for an oldsmobile that ran like crap because half of the cam lobes were on center where they should be, and half of the lobes were off center. Machining mistakes happen. Nothing we did would make that car run well because the cam was ground incorrectly.

The hydraulic lifters are very forgiving to adjust the valvetrain even if all the specs aren't dead on. There are a good many of domestic engines that have no provisions to have adjustable valve trains. Those engines have mild hydraulic cams installed all the time without going to an expensive conversion to make the valvetrain adjustable.

While I'm not against making a Pontiac valvetrain adjustable, I don't belive that this is the OPs problem, rather that it's a cam timing issue. I have installed more than a few mild performance cams into Pontiac engines without making the valvetrain adjustable, the lifter travel made up the difference to make sure all the valves were seating. If the new cam has a base circle close to the OEM cam, it should work satisfactorily with a non adjustable valve train.

Years ago I worked on a 66 Catalina that ate the nylon timing gear teeth, when it was replaced it inadvertantly was one tooth off. The car idled just fine, but was about as gutless as a 6 cylinder full size car. After resetting the cam timing it would fry the RR tire off. Cam timing has a huge effect on performance.

I'm curious also of what carb, and intake the engine has on it, the wrong intake, with improper gearing can make a car gutless as hell because of the runner velocity is wrong for the combination. All the parts have to be in harmony to gain performance. Transmission, gearing, intake, and carb, and exhaust system, would all be helpful to know before condemming the non adjustable valve train.