jay d - To answer your question on piston wall clearance specs, the 1955-59 GMC Model 100-500 Shop Manual calls for 0.00325" measured at right angle to piston pin (see screenshot below). I can't recall what year your 270 is??? For further info and detail on the 270 maintenance/overhaul and specs, read through
Section 8 of the Shop manual for that year group. If you need info from earlier Shop Manuals, let use know what year engine you have so we can see about finding more out.
Please note this is stock cylinder wall clearance and your needs with a blower, and probably more modern piston design/materials, may differ.
I didn't really find much more on your engine question in Stovebolt, but did come across this
related conversation in the old "Inliners International" Forums that might be of interest to you.
