If the heads are stock, with factory rotators and guides. You are pushing the limit at .575. Most of these heads have a short valve spring/retainer setup and it is hard to come up with a spring installed height of 1.875 that is required for much more lift.
Usually I take a rotator eliminator and trim the back of it. Plus use an aftermkt retainer or .050 up lock to get the proper height.
Also, while doing the spring work. I trim about .100 from the guide tops and cut for seals.
what is the max flow any one got out of these heads, stock is 256cfm i think. what if you ported them out and put in 2.19/ 1.88 valves. what rpms could they flow up to?? what could be the max port .cfm's
I put 2.19 and 1.88 valves and hard ex seats in all 049's and 781's. Bowl hog out to inner seat area, blend sharp edges and open bowl and blend short radius. Port match intake and smooth out top 2/3rds of exh port.
I have never had any flowed tho. Most of the cams I use in these heads are around .620 lift. Any wilder than that and I go for aftermkt 320 heads.
I have some cams in the .700" lift range using .875" and .904" tappet diameters for solid flats. I have a customer that is limited to OEM casting in a pull truck class. The 781's with extensive work will reach the low to mid 300 cfm range on the intake side. The class is limited to 470CID limit and these engines get turned to 8000 plus so the cam has to be pretty big.