I always straighten out the tin pan and only put silicone here, 1/16 inch does it, the CI pan rail is for sure flat and smooth, therefore should not need anything on top of the gasket. If one puts gasket material between the CI pan rail and cork gasket, one is looking at a hard and messy job removing the pan.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.