Pletch,
I cannot find tune-up specs for a 228 on
Rob English's oldGMCtrucks website; however, I'm dumb enough to try to answer your questions (and, I hope and I know that someone will correct my errors - I just hope it comes from a GMC person who knows the 228):
1. "Dwell/point gap specs (I have found between .016 to .022) and 26degrees to 33degrees. I know these number are all close but what should I use."
-> Go for the middle number; but, if you have new points, use .022" and check the setting(s) after 500 miles (many people reset every 1,000 miles thereafter).
2. "Ignition timing. I think I found that it should be 5 btdc at 600 rpm. Is this with the vacuum hooked up or not."
-> I do not think that you need to worry about the vacuum hook-up but I am not certain about any/all 228 carburetors: WHEN IN DOUBT, it never hurts to disconnect the vacuum line to the distributor and plug the line on the manifold side of the line. My uninformed understanding of the 228 timing is to set the distributor so that the clutch-housing-pointer points to the "U" on the flywheel. I hope someone with a late 228 will confirm or correct.
3. "Then I'm reading posts about 3450rpm and timing should be 32.5-39.5."
-> I do not know what this means. Maybe this is referring to total ignition advance at 3450 rpm? Someone else can address this one (and split a few hairs)
Tim
