FWIW, for a data point on the chamfers leaking: My son's 340 was a virgin block, with the chamfers, and the lifter bores were unworn. (A couple were so tight that we had to get Crane to send us a few extra HFT lifters with OD on the small end of the range, so we could fit them in some of those tight lifter bores.)
Fired it up with the drill to pre-oil and check oil to the rockers (since I had added some rocker oiling holes), and did not see any real oil flowing/oozing out of the chamfered bores at all. So, from that, I wold suspect excess oiling there simply has to do with bore wear. (Test conditions: Oil was 1W30 at room temp, with a drill at 600 RPM, which corresponds to 1200 engine RPM. Pressure was a bit over 70 psi at the usual pressure sensor location.)
