The lubrication system is indeed a problem. It and the thin cylinder walls are two not so amazing aspects of an otherwise amazing design. 
The small block Fords have a 3 passage lubrication system, the Cleveland design went backwards with a 2 passage lubrication system. It should have progressed forward with a 4 passage system. Obviously a financial compromise was involved. I don't think the engineers would have designed it this way willingly, the 2 passages must have been agreed upon in committee in order to secure some other aspect in the engine's design. That's just a guess, but it seems plausible.
The manner in which the main oil passages intersect the tappet bores creates large ports in the sides of the tappet bores. Few people comprehend just how severely these large ports impact the Cleveland's lubrication system. They disrupt the flow of oil to the crankshaft, they create extreme leakage at the tappets, they create tappet incompatibility issues, and they give rise to excessive valve train lubrication.
These issues manifest as under-lubricated rod bearings and low hot oil pressure. They are not horsepower related, but more or less rpm related. The lubrication issues are at work, robbing lubrication from the rod bearings, even at low rpm. They worsen as rpm increases. They become so severe above 7000 rpm that bearing failure occurs.
The external oil line between the oil filter passage and the oil pressure port does not resolve the problem. Tappet bore bushings resolve the problem because they eliminate the large ports between the tappet bores and the main oil passages. In fact I like the Cleveland lubrication system better than the small block Ford lubrication system once the bushings are installed in the tappet bores.
My formula for the lubrication system is as follows:
• Utilize 10W30, 10W40, or 15W40 synthetic motor oil
• Install a wet sump racing oil pan
• Install 16 tappet bore bushings (with 0.062-inch orifices)
• Chamfer the oil holes at the crankshaft journals.
• Install heavy-duty, fully grooved main bearings; Clevite # MS1010HG or # MS1010VG. If fully grooved bearings (G suffix) aren’t available, improvise by using the upper shells from two sets of standard Clevite # MS1010 main bearings.
• Install heavy-duty rod bearings; Clevite # CB927.
• Set the bearing clearances and rod side clearances to promote lubrication:
a. Main bearing clearance = 0.0025 inch to 0.0030 inch
b. Connecting rod bearing clearance = 0.0025 inch to 0.0030 inch
c. Connecting rod side clearance = 0.018 inch to 0.022 inch
Moroso sells a restrictor kit for the Cleveland lubrication system. It contains 4 small restrictors for cam bearings 2 - 5, and a larger restrictor for the left hand oil passage. The larger restrictor has led to the random collapse of hydraulic tappets on the left-hand side of the engine. I wonder if this might explain the collapsed tappet your Pantera's engine recently experienced?
I've explained all of this this a bit more thoroughly in the thread linked below:
https://pantera.infopop.cc/topic/1598208420299384
-G