The issue with rev limit is actually cam timing related mostly. The earlier four bearing cranks, which were actually heavier than the seven bearing cranks, were unable to rev without a torsional period that shook everything loose. By the time of the 1978 200 crank, 3M casting I think, the period was shifted up far enough for you not to run into it. The log head best crank for best rev range is the Aussie 1993 EF crank, a 12 counter weight item, similar to Holdens 12 counterweight 3.3 crank. Ford Australia then downgraded that crank to another type when they sorted the main bearings and oiling system.
In a similar way, the cam timing on the 1985 Aussie 3.3 122 hp Holden created vibration at 4500 to 5500 rpm, but when the breathing and induction and extractors were added for 142 hp, it reved like a top to 5500 rpm and beyond.So if you cam it up, carb it up, and improve the exhast, the same thing happens. This is especially true of earlier Holden engines with there poorer Red motor crank...the 202 was always a vibrstion ridden un reving hulk, but when a set of triple carbs, small chamber head, headers and wild cam were added, it took off, with the two slight harshness periods at 4600 to 5300 not noticable when the engine reved so quickly. When the steel crank or later blue motor 12 counter weight crank was added, the vibration period was at 7500 rpm, so it was okay for racing to 7000 rpm.
The Australian and Argentine 221 and the US and Australian 250 were bigger engines, with the same 8 counterweight cranks as the 200, just longer stroke and bigger main bearings. The tests from Bill Santicecine for Ford in the late sixties said that the crank was okay to 7500 rpm, with forged rods, only the bolts were and issue, and noted that the oil pump might need uprating.
The Aussie cross flow 250 OHV six, and the canted valve Hemi 3939 cc 239 cubic inch OHC, which both have the same crank, is that there is a torsional vibration period exists at 4600 to 5300 depending on the cam timing. The British Prodrive/Tickford (Aston Martin) engineers who did the first 1992 216 hp at 4600 rpm XR6 said the stock 250 Oz crank was marginal at 5000 rpm, and Ford Australia had to upgrade the crank when the 3984 cc 20 thou over 4 litre six came out.
The point is the canted valve engines (1976-1992 x-flow, and 1988-1992 OHC'S) 'created' a vibration problem that didn't apparently exist on the earlier non cross flow engines. This was also noted with the canted valve Clevelands verses Windsor V8's...changing the heads to flatter angles suddenly created more power from less shroading and larger vlaves and a shorter flame path, but more detonation and vibration. When an engine is detonation limited, this is a reason why the canted valve engines like our Aussie X-flow are not always best.