I have a 1981 Schwinn Super Sport. Last year I respoked both rims and while I was at it replaced the hubs (dynamo{front**, 8 speed cassette{rear**). Now I am in need of replacing the bottom bracket (It is pitted and worn). Right now I have on the bike the original SR Apex triple crankset (170mm with 34/46/52 chainrings) and the spindle measures are A=34mm B=51.5mm C=42mm. What would be suitable modern replacement?