I think that clamping the barrels with the case is a poor way to proceed. I have never done it, but I certainly do not know as much as P.E.I. The liners are too thin to clamp at the waist and the crankcase will distort the liner significantly. Some builders "hot hone" their cylinders in the cases to avoid this, but that seemed too complicated to me.
I have had good luck with ten thou clearance for the crankcase spigots, but it is too big a gap for the oil to transfer through the liner hole. This was a good reason to discontinue the use of the oil hole. Two of the racing 500 singles have cylinders that were plated 30 years ago and are still being used today as they remain within their stock racing spec. The Nicasil appears to hold up well without oil holes or clamping. The piston skirts were set at 0.0035", with the Nicasil aluminum liners and 0.006." with the nodular iron liners.
David