Shellac is used to hold gaskets in place. Most if not all of the sealing is done by the clamping force on the gasket.
RTV is a vulcanizing rubber and can be used in place of a gasket. In this case Garret is using it very thin in case there are irregularities or other issues with the surfaces. be very careful not to use too much. Bits of RTV that come off inside (fill in the blank) can cause issues down the road.
Not much to add. I would not use the 360 intake with a 318. Much more important to keep air velocity high than it is to increase volume. A late 318 factory 4 bbl intake would be OK. Regular Ede Performers are fine and will save weight. Is '91 still a copper and brass radiator? If so, use a coolant with conventional inorganic inhbitors , not universal which are HOAT.
