GLEN - I think the # is a SignalStat #525...any autoparts place should have them.
CURTIS - Early K161's only had 2-7/8" dia pistons and the later ones had 2-15/16" but they were both 7 hp... So Yes, if You have a .020" 2-7/8" bore You can probably use the 2-15/16" stock size pistons plus their oversizes. The K181 was the 8 hp engine and they were all 2-15/16" bore but 2-3/4" stroke as opposed to the K161's 2-1/2".
CURTIS - Early K161's only had 2-7/8" dia pistons and the later ones had 2-15/16" but they were both 7 hp... So Yes, if You have a .020" 2-7/8" bore You can probably use the 2-15/16" stock size pistons plus their oversizes. The K181 was the 8 hp engine and they were all 2-15/16" bore but 2-3/4" stroke as opposed to the K161's 2-1/2".