No problem with using just a gasket between the carb and the intake. The original 273 HP used a 625 cfm Carter 3855S, for what that's worth to you.
I hate to be a party pooper, but I'm a bit suspicious. My suspicion is that you have something other than the HP engine in the car, regardless of what the VIN says. It makes no sense to me to put a 2 bbl on a high compression engine. Also, if your avatar is of your engine, the finned applique valve covers that came on the 273 HP cars are gone. At the very least, some monkey business has occurred as the two most visibile identifiers of the HP engine are not present.
The factory HP cam had .425 inch lift. If it's an HP motor, you should get that kind of movement at the lifter or push rod. The other way to tell, as 64Cuda says, is to look for the domed pistons. If you have or can find someone with a lighted borescope to get in through a sparkplug hole, you'll be able to tell without popping the heads. The piston will be either flat or domed, if they are original pistons. The whole package of cam, carb, and compression boosted the 273 from 180 to 235 horsepower (gross, at least in 65 & 66.).