We just received our Jesel rockers and they also say where the adjuster nut should be in relation to the number of turns in/out on the instruction sheet.

I put a full set of Mantons on my blower motor recently. Cory just built one with the steel crower rockers. Results to follow...

T&D aluminum on my 250 blower 598, no issues but rockers were new with the build so 300 runs or so. 1 piece intake stand.

If rockers are breaking for no apparent reason, they are old and need a rebuild, or need to be tossed away. Aluminum rocker bodies will deform over time if you have enough spring pressure and lift after many cycles, how many nobody knows. Rebuild every so often, if the new axle bearing goes into the rocker really easily and doesn't have a slight crush fit, the rocker is too sloppy to re-use. Good spare, but not for a fresh build. If chromoly or steel rocker, that shouldn't happen unless there's other contributing factors, but bearings can and do get old and need to be replaced.

I have seen success with much more common parts. Chromoly comp cams stud mount rockers, stud girdles, BB2X head, 800 lift, 3/8" pushrods 0.165" thick, 350+ lbs on the seat, PAC 1248 spring. 522, 14:71, 4-teens 170+ mph, 22-28 PSI Boost, 200 hundred runs, no issues. Sold the motor at 200 passes so not sure what happens beyond 200 runs.