According to the 69 factory manual the pan to case torque: 12 ft/lbs. [M40 trans sect. 7E] As with any pan style gasket, all surfaces have to be oil free. And, use a cross bolt torque pattern, making 2 passes.
BTW, I wasn't suggesting using an OMG big hammer. I have a hammer that's similar to a body hammer and back that up with an aluminum block.. Another technique is to use a pair of aluminum blocks and vice to press it back into submission. I have a vice with aluminum jaws, so it's quick & easy.
I have a hammer that's similar to a body hammer and back that up with an aluminum block.. Another technique is to use a pair of aluminum blocks and vice to press it back into submission. I have a vice with aluminum jaws, so it's quick & easy. 
