Just out of curiousity, where did you get the 427 block?
If it came out of a race boat or actually the crank came out of a reverse rotation boat motor, they were built to spin in reverse.
If you install a reverse rotation crank and spin it in the normal rotation, the little groves on the rear crank seal surface will pump
oil toward the seal and flood it causing a leak. Normally the machined grooves are designed to pump
oil away from the seal.
Laying on you back, looking up at the rear main seal surface of the crank, the crank spins left to right (counter-clockwise).
The grooves should look like back-slashes ( \ \ \ \ \ \ \ ). If they are going the other way,
oil will be pumped toward the seal. Also, are you installing the seal with the lip in or out? Out is wrong! The lip should face in toward the crank. Incorrectly installed and the internal pressure of the engine will blow oil out the rear.
Doc