HI,
If you are looking at lowering your CID why not just go with a 28 OHV Briggs motor. Shortening the stroke is really going the wrong way in this motor. I know we have talked before but the problem is this. YOu don't have a rod availible to make things match up.
If you have a CID rule and it is only 30 CID then 28 Briggs is the way to go. Briggs 28 is really 28.4 and a 31 is really just over 30 anyway. So you don't gain much.
Just a thought.
Don