Broke rocker arm..

[RICK LAKE]

DIRTYDOG427 Pictures tell us alot of what happened. here's some ideas without see the rocker arm, are the arms aluminum or steel? Location of the break helps too. Is the riding surface of the shaft blue?
Going by your story here goes You said the motor needed over size cam bearings? I have not heard of them being around. If the bearing spins even a little on the #2 or #4 cam bearing you loose oil to the shafts. Since it was an end one, you may have no oil pressure to it and it just broke from heat and no lube. This is the reason for a picture. This rocker could be 20+ years old and just got fragile over this time and cracked. Next would be to check for coil bind on the valve spring. You want about .100" clearance between the coils. You can go as low as .060" I don't recomend this tightness.
The end support might not be seated and come loose and rocker everytime that end rocker goes through a cycle. The shaft will flex and the rocker will edge wear and break. Pushrod rubbing on the intake manifold hole can break the rocker if the pushrod is not centered to the rocker and the ball in the adjuster end. The hold down bolts, for the rocker shafts may have loosen, with out alot of oil going to the rocker arm pivot area, again over heat, hot spot and snapped.
I am going a little off base but this all comes back to possibility of the same problem, poor or no oiling to the rocker shafts. What is the oil pressure on the car in both hot and cold startup? Also what is the pressure at 2,000 rpms. I don't need this to the last pound but feel that you have little to no oil pressure at idle to the rocker shafts. Just because the gauge reads 30 psi at idle you may only have 5 psi at the rockers. IMOP if you are not running a HVHP oil pump with a MIN of a #60 psi pressure spring, the motor will not last. An HVHP oil pump with an #80 pound spring would be alot safer all the way around. This is not a small block chevy we are running. An FE needs alot more oil pressure and flow because of the way the oil goes in these motors, that is except for a side oiler. Also after repair get a bottle of Lucas oil suppliment and add this. Its a clinging oil and helps on startups. Quiets the motor and rocker arms down too. Make sure you add this with the motor warm and pour slow and let run for a couple of minutes to get a good mix. Also add 1 extra quart of oil to the motor. The returns are slow on the FE motors. It will not hurt anything and always keep your pickup in oil and not sucking air. You might still have a problem with camshaft bearings unless they where pinned in location. I will hope for old age. I would replace the set and buy either Harland-Sharps, Look around for a set of Ersons, or the replacement of the erson setup. They are not cheap but the motor is worth 10K, if you break it do you have another bullet in the garage? Don't go cheap on this part. Also add limiters to the rocker shaft openings to about .080-.090" oriface to control oil to the bottom end and keep more down bottom. This is ONLY if you repalce the oil pump with an HVHP one. Rick L.