If you have the AIM, look at K24 A2, or page 267 as penned in on my copy.
I believe the bolt goes thru a flat washer, then fiber washer, then thru the tube assy then another fiber washer on the bottom. I recently bought a repop set and their fiber washers are black. Had to buy from an early 60's Chevy parts vendoras a road draft tube hardware set. You also may want to ensure you have the tin can looking vent under the intake, that connects to the same passage inside the rear of the block.
I found mine can't be installed until the engine is dropped in, as the rear lift shackle is in the way and will need to eventually come off.