O-rings only between pump and cover. O-ring only between block and pump if using the Milodon pump. If you use the "sandwich plate" then you use a gasket between the block and plate and another gasket between the plate and pump. OOPs  Never done it that way but never had any issues either  Milodon billet pumps #21814, if that makes any difference.
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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