Unless things have changed - you can get assembled heads from various shops - but not from Engine Quest. Out of the box they are only bare castings. They were designed to be a service replacement for cracked but operational factory heads where you would just re-use everything.
So in my opinion things like flow data, and quality of parts can't really be guaranteed accross the board as these will vary with the other parts chosen.
In terms of lift - .600 at the valve, with a 1.6 Magnum type rocker, is limited. That only leaves you actual cam lobe size of .385" or so. They are limited because they don't have deep enough spring seats to cut down and get a taller installed height. Factory rockers don't work wel with taller valves which means a more expensive rocker setup - one that can push the overall " on the car and ready to run" cost similar to an LA based aluminum head. So they are great for factory displacements that are destined for mild to mid-sized cam. Great head on the right engine. Great "as delivered quality. But limited when looking at larger displacements or higher rpm power levels. They are a great fit for the OP's intended use.
Sorry, but I sell 4-5 pairs of EQ a week. I personally know their sales staff and exactly what parts go into them. I also know Howard as Vegas Machine and Crankshaft , which is where EQ gets all their assembled heads built at. They assemble most of our heads as well. I dont believe that swapping between valves will affect flow of the head in anything but tiny amounts, and that would only be with a back cut or necked down valve stem. You would be taking about numbers so small that it would be tough to measure. I have sold hundreds of pairs and can tell you that I have never seen as much as a few cc's difference between ports or heads. I doubt you could find a difference of 3 HP between heads that are OOTB and not cleaned up.
You say you cant cut spring seats in EQ enough to get springs for big cams ? OK...I know a guy that runs over .600" lift with a 5.2 and EQ heads. Its stroked to 379 I think and it runs ridiculous times in a small tire fish. This engine makes over 580HP.
The front cover of Car Craft has a 5.9 build done by member here , IMM, I believe and its 450+ HP and 450+TQ with nothing more than a piston swap(for valve clearance), EQ heads w clean up, cam and not sure which intake. Will be out soon. Perhaps then you will change your mind. These are not mild build heads, they will run with the rest of them if not more.
Back to OP, he clearly stated that he was dead set on 268, so he could easily use the EQ OOTB with springs for $949 and a set of factory rockers for cheap or a set of roller tips with studs and push rods for $299. Hell we paid almost that much just to fix the last few sets of Edelbrocks before they got installed. I prefer the EQ on a street build, they make a bit more torque down low.
If you get the LA Edelbrocks, they are more $. Summit is right at $900 for cheapest Ed. Thats more than a bit compared to $1248 pr ready to go with CrMo .080 pushrods and roller tip rockers, comp studs...
IMHO, putting $800 in old shaved low comp heads with 2.02 " intake, hoping to get comp to 8:1 is just putting a pig in a pretty dress(and keeping drag racing machinist working), it will still be a pig. It will be a low comp small cam 285 HP engine. Those heads could easily crack after enlarged, valves, port work and a .050" shave. Hate to see good $ thrown at old outdated parts. And to clarify, I am not trying to sell him parts, he can get them from Jegs for $10 more, I am plenty busy, I am offering the best advise for the question asked and to get him as close to his HP goal as possible, which will be approx 325-240 HP with EQ, not open chamber ones.
