What carb is on a 73 198?

There is no early 1920 vs. late 1945. All of the '73s got Holley 1920s. The 1945 didn't appear until the start of 1974-model production.

"Remanufactured" carburetors via parts stores in person or online are junk -- do not buy. If you need an off-the-shelf solution or want to send your carb in for full refurbishment, this outfit at least says all the right things, and results seem to have been better than with the parts store garbage.

Do note that the Holley 1920 carb eventually reaches at hard end of life and no amount of tinkering brings it back from the dead...the metering block has blind passages that get full of "metal mould" corrosion and can't be cleaned. Doesn't sound like yours is that far gone, though. Also, the throttle shaft bushing area of the body casting gets wallowed out, which makes the engine run poorly until the shaft is rebushed as described here (that linked carb outfit above does this, too).

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

It's grown difficult to get hold of a good-quality carb rebuild kit. The ones from www.daytonaparts.com come with a much better-designed inlet needle/seat than other kits (they call it the "DFV" for Daytona Float Valve, but it's just a reissue of Tomco's S7 valve…no matter what you call it, it's still better than the kind that comes in most other kits). You don't get a real float gauge with anyone's kits any more, just a useless strip-of-paper ruler. New float for the 1920 is still available from Walker, their part number 100-14.

You'll get rid of a lot of off-idle stumble and mushy acceleration by bypassing the OSAC valve: find the hose that runs from carburetor to widget on the side of the air cleaner housing and from there to the distributor. Take the widget out of the loop, run the hose directly from carb to distributor.

And take care of other tune-up factors, too; pay careful attention to spark plug selection and installation and to valve adjustment -- tune-up parts and technique suggestions in this thread.