If it's got the 3 bolt throttle body, it's probably a Holley 94 from a Ford flathead V8- - - -239 cubic inches. Pretty good carb, and the calibration will be "close enough" to use on the 248. It's nowhere near the quality of the Zenith, but it's not a bad carb. I ran them on my 47 Mercury with a 255 cubic inch bored and stroked flathead and 11.25:1 compression.

The first 3 digits of the stamped engine number on the machined pad behind the distributor gives the cubic inch displacement of a GMC inline six- - - -228, 248, 256 (rare) , 270, or 302.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!