Using a 228 carb with an adjustable metering jet on a 248 worked just fine for us 50 years ago on rural Texas roads. Running a slightly over rich mixture gave us much longer valve life and actually did a little better on fuel economy because the 20 cu in saved a gear on a lot of hills. We used C45 plugs to compensate for the richer mixture. Carburetor icing was however more of a problem, but it was only around 38 degrees and high humidity. I agree, however, that a 228 carb would not work on a 270 with good results. I have put Stromberg WW carbs from a 56 Plymough on a 270. If you have a 3 bolt manifold, a Holly from a 272 Ford works well on a GMC 270 also.
