Mike, the numbers are not as useful as allowing a date. They do give info as follows.
C in an octagon indicates manufacturer, in this case American Steel Foundries in Chicago.
E4186 is the Ordnance drawing number
2A 1653 is the part number
LO and BU1176 are the heat numbers indicating grade of steel and final treatment.
It is almost certainly a 1943 built example and the 35 ton weight is, as you say a little heavy, 35 US tons battle weight is right. I doubt it weighs 20 tons now but it must be getting close, that engine pack is 2 tons alone.