O.d.

2 jpar and one of those was a 390 ford in 1967 fastback mustang. no reason to ever want to see another. flywheel explosions are very rare today. This is due to better metals and better heat treating. That said it still happens. you don't see it because scatter shields are mandatory in most classes. the clutch/basket is just as dangerous

451 is 400 block with a 440 crank. mains are turned down to 383/400 standard. counter weights are also turned down. what we did before stroker cranks became the norm. Made high revving low deck that appears like a stock 383 in road runner etc. Not a good option today as chinese cranks are stronger than mopar factory cranks. especially once you turn through the heat treat on a factory crank.

To the op sorry for getting your original post off track. I would not run a overdrive behind anything other than a very mild small block. And then only if it was rebuilt. They are very desirable for some of the parts that they have that can be used in a standard 4 speed.