If it was ONLY the #8 cylinder that was the problem, it would have to be a problem with the valve adjustment on that one. Who did the rebuild on this? Did you have a temp gauge on this (hope so) and what was it reading? The hose coming off could have been just loose, and the pressure blew it off...Im hoping it wasnt because it overheated, cause if it did, you might have other problems. Start by pulling the valve covers and adjust all the valves again, right thru the firing order. As you bring each cylinder up to TDC on the compression stroke, feel the rocker arms for excessive movement before you adjust anything. That will tell you if you may have damaged the cam or lifters. If there is a lot of clearance at this point, investigate further. Re-check the plug wires as far as placement, and make sure the ignition timing is set properly. Many guys dont have enough advance during start-up, and this causes it to run hot. ( But not just on one cylinder) You can have a lot of advance on break-in as there is no load on the engine. John