Thanks for your help Jon , the eraser was good.
If I hold my mouth right and use my fertile imagination , the first number may very well be a 9.
The outer numbers show good as 2135998
So the chances of it being a 270 carb are good as I have never seen another sized GMC engine in this country.
I have still got the original W-1 and perhaps I should make the effort to stop it leaking (especially from the copper plugs) but the local carb shop is a challenge to deal with and my chemical sensitivity makes dealing with fuel risky. Such is life, eh.
Oh, if it's a 270 carb , that would explain the mpg change
