Sealing the oil pan 100% is probably the most frustrating part of a Gen 1 block in my opinion.
I'd call Canton and get their advice.
Is there gasket silicone and metal reinforced?
Did you anally clean the block surface, degrease, then solvent wipe?
This is the product that appears to deliver the best result if clean.
That said.....the machine shop that rebuilt my motor and installed a new Milidon pan with FelPro silicone/metal gasket using The Right Stuff managed to make it leak front and rear......