I just went through all of this for my X flow head. for my intake, I Found a BBC exhaust valve that was 1.880/5.300 long w/ a 11/32 stem. I had my machine shop turn the valve down to 1.800, otherwise it was the exact same length as the stock valve.
Used a SBC 1.5" exhaust valve that was 4.960 long same as xflow across the board.
Used BBC beehive springs , and they got installed at 1.800,..but I used a spring cup and a shim to get that, as the stock installed height is closer to to 1.900.
Additionally, I used a pushrod guide plate kit from Crane cams that fit the existing pedestal bosses, and the stud has a 5/16 coarse end that screws into the head, and a 7/16 fine thread other end for the rocker. I ended up having my head tapped to 3/8 and used a different stud that I modified as my cam is a solid roller, and I wanted a stronger stud anchor for the rocker.
I used a Comp Cams 1.73 roller rocker for BBF on top of that.