The 228 GMC engine is similar but very different from a 235. I don't think a part will interchange, except maybe the rear main seal. You will need a rebuild kit specifically for a 228. You may be able to find what you need from NAPA, CarQuest, O'Reilly or other chain stores. Many of the vendors listed on the links page of this website have GMC parts. Try Patrick's, Rock Auto, Jim Carter, and others. Also try the oldgmctrucks.com website for GMC specific info. They also have a great forum with lots of knowledgeable and friendly folks.
Good luck!
