In the pix I just posted, one shows the dual chamber oil bath air cleaner which is normally mounted on the firewall, but removed to work on the carb. The left engine bay pic shows the formerly used selenium rectifier and large regulator for the charging system. The truck now has an internally regulated alternator. The 503's were made from 49-59, used in 630, 660 and 670 series trucks. The mid 50s had the huge Holley 2bbl as seen in pic; the late 50s had a Holley 4bbl (a modern double pumper bolts right up); the early 50s had a Zenith. The later engines had little coolant squirters in the head, aimed at the exhaust valve area. The block is a 2-part, with the jug section bolted onto the lower section.
