What Indy meant was they have 2 different sleeve OD sizes. One they use for up to 4.440 bore and one they use to 4.500 bore. Why they would use different sleeves is beyond me. Just put the 4.500 bore sleeve in and start at 4.350. Let the customer decide the bore size and have a thicker sleeve wall at smaller bores. More cylinder stability. If I was you at that HP level I would use a cast solid block minimum. IIRC Big Time Bob with the orange procharged Dart broke a Indy water block. Might want to PM him here or on YB.