Here is the best way to seal the rear of the pan. Forget any type of rubber seal, they have a BAD habit of squishing out and starting a major oil leak. I cut a custom seal from a piece of 1/4" thick rubber impreganted cork material. It's available on-line.
Then just apply a dab of RTV to the ends, set the pan and not one drop of oil will every get past it.......
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https://cliffshighperformance.com/
73 Ventura,
SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),