Thanks for the reply Brian. New to the site (and Rochesters) and any and all help greatly appreciated. My thoughts were to rebuild the one that was on the car as I bought it - the 1705922 as "practice" and to get familiar with these carbs.
But if I'm going to rebuild one maybe I should look for a 7042202 core to start with ?
I already installed the replacement carb and it seems to work fine. Very slight off idle stumble. Why would I not use the 17054927 if GM used it as a replacement ? (Anything other than originality ?)
Car as a one owner out of Texas. Apart from the carb and the ignition coil it appears to be numbers matching. But at the end of the day, it's only a base model (although fully optioned up, leather interior PW's etc) so, not an LT1 or anything special. (Well, yes, it IS special to me)
By the way, I'm in Brisbane Australia.