The exhaust lifter is usually the first to go as it sees the highest load. It's possible it wasn't even the cam/lifter's fault. Something like a weak pushrod or rocker stud can induce flex in the valvetrain that shocks the lifter. However, it could just be straight up load.
Say you have a 1.72" exhaust valve with a stock cam that opens the exhaust valve at say 70° BBDC with ~100 psi cylinder pressure. That pressure is multiplied by the valve square area. (2.32 in^2 for 1.72" exhaust valve)
2.32 in^2 x 100 psi = 232 lbs resisting the valve opening
Then tack on the valve spring rate which a stock spring probably only has ~80 lbs on the seat.
232 + 80 = 312 lbs at the rocker tip
Then that's multiplied across the rocker ratio as it's acting like a lever arm in this case. (1.7:1 for BBC)
312 x 1.7 = 530 lbs on the lifter that must be overcome just to lift the valve off the seat.
Now apply it to the Melling MTC-6 camshaft that you have. It's 288/298 duration @ .006" and 204/208 @ .050" which is really weak. It's on a 112 LSA. (straight up)
The exhaust valve on that cam opens at 86° BBDC. At that point, the cylinder pressure is about 160-180 psi. Let's assume you're upgrading the valve springs as well, as you should, and the seat pressure is now 120 lbs.
2.32 x 160 = 371 lbs on valve face
371 + 120 = 491 lbs at rocker tip
491 x 1.7 = 835 lbs on the lifter
So that cam, despite being on the weak side, induces +57% more load on the lifter. That must be considered with that long duration, weak lobe. I recommend putting in new pushrods, beefier ones, and better rocker studs to keep flex out of the valvetrain with that load. A stock pushrod can flex really easily, especially on a tall deck BBC.
On to the oil choice and break-in...
I never recommend oil supplements. The way I see it, if you have to add something to your oil, then you're using the wrong oil. Forget that supplements exist and just run a proper oil.
For break-in, I'm partial to Driven BR30 break-in oil though Amsoil's SAE 30 break-in oil and HPL's break-in oil are great choices as well. They contain a proper additive package for the break-in.
Before starting the engine, I preheat the oil in the pan with a pan heater. You can use a turkey fryer or something and pour it in after warming, doesn't really matter how you get it warm. This makes priming the system much easier as the oil thins out a good bit with the heat. It also benefits ZDDP since it becomes more reactive with heat so you're giving your anti-wear a kickstart to start protecting as soon as possible.
This part is important... make sure you have everything good to go before you try to start the engine. Make sure the carb is somewhat tuned okay enough for it run through the initial break-in. Make sure your spark timing is correct, not 180 out or something of that sort. Make sure the balancer isn't faulty and giving false timing mark readings. Make sure you have fuel flow and pressure. The reason for all of this is because you can wipe the cam lobe just trying to start the engine. I've seen it happen quite a few times where someone is sitting there cranking the engine over and over and over trying to dianose why it won't start. Meanwhile, that cam is grinding itself down with no oil splash. You don't want to do that. If it doesn't fire within say 3 seconds, let off the starter.
Once fired up, go to 2500 rpm for about 30 minutes. There's several reasons for this. 1) It puts more heat in the oil faster to get ZDDP working better. 2) It ensures good oil splash in the valvetrain and on the cylinder walls for the break-in. 3) It gives more piston speed to get the rings into EHD and HD lubrication so they don't glaze the hone while you're breaking in the cam. (this only applies if you rebuilt the engine with new rings and hone) I ensure the coolant and oil both reach 200°F for a minimum of 15 minutes, usually using delayed spark timing to heat it up faster and then switching to manifold vacuum advance to maintain the temperature once warm and keep it from overheating.
I like to heat cycle the engine. Some don't. It's really not necessary in most cases, but I like to do it anyway. I shut it off to cool all the way down to ambient temperature naturally.
Then I preheat the oil again, start it back up, go back to 2500 rpm to get it heated up quickly, and then start making loaded pulls at WOT with varying rpm. (as tuning will allow) Never let it idle. The worst thing you can do to a fresh engine is let it idle. I make several WOT runs, showing it no mercy. This can mean driving it out on a desolate country road, putting in 2nd gear and flooring it from say 30-50 mph, and then coasting back down to do it again.
After that, let it cool all the way down again, and then remove the filter. Inspect the filter for anything unusual. I'll check rocker alignment and lifter preload and do a compression and leakdown check at this time. If all is good, put a new filter on, top off the break-in oil, and go 100-250 miles. Vary the rpm and load through this time. After that, the break-in is done.
