Ported heads on a GTA?

Would this make any noticeable difference on a healthy atmo engine with John Law Holley conversion, but standard cams and exhaust?

The Holley conversion has made the car noticeably more responsive, especially engine breaking/when backing-off.

Engine braking ha ha.

It makes the car reliable and also more economical and a lot more responsive, the engine braking is no different you must have a sticking brake or something, feel the wheel hubs after a run and see if one is hotter than the rest.

Sorry, I meant that when you come off the accelerator, you 'feel' it (the decceleration) a lot more. So, the car seems to respond more quickly. The brakes etc are OK.

Has anyone had PRV heads gas-flowed?

On mine I did the Headwork the thing is you can improve the exhaust buy removing the big aluminium lobe which slows the gases down for I emissions, which is a big improvement however the inlet manifold is not that good.
I always look at money payed for HP/Torque improvement, £300 approx for a cam reprofile which will give a big gain as the standard lift is poor, that’s the best money spent for good gain.
If you want to spend big change the inlet valves for the later heads which I think are 43mm compared to your 38mm, I’ve been working on old Citroen stuff so I can’t remember the exact size.
Personally I just worked on the shape of the inlet port and the results are impressive for minimal cost but you do need to no what you are doing as it can lose you performance.
A lot of people chase Hp but for road driving and overtaking Torque every time over Top end Hp, so for the money do the cam and some light head work but the heads might open up a big can of worms when you take them off as there are liner issues which could come to light.