I have never used any kind of lubricant (or sealant) between carb spigot and intake rubber. If the sizing is correct, there should not be any need for that.
On the cylinder head flange connection, I would use Threebond or Permatex #2 or #3 (never silicone sealant!) on both sides of the paper gasket, when a gasket is used. On the straight intake rubbers I use on the XS, there is an integrated o-ring, so on those I assembled without any compound.