79, 403 lifter problems

Hi, I just got new headers, and by eliminating noise from the old leaky ones, I have come to find out that my lifter on the top left side (next to the alternator) of the engine is knocking profusley.
I was wondering, how much of damage can be done to the car if I drive it and should I even drive it????

I would suggest not to drive it. If the lifter has just collapsed, not much damage will occur, although the looseness is hard on the rest of the valve gear for that one valve.
However, bad lifters usually make a clicking sound. If its 'knocking profusely' maybe its something else, like piston slap or a bad bearing. In that case, do not drive it at all. Sometimes its hard to tell. I have seen bad mechanical fuel pumps make a knocking sound as well.

its a clicking sound, and the mechanic told me that sounded like a lifter.

The ticking noise was the back two rockers as long as their assemblies, and right now I am replacing them with the new ones.(they were worn out). Anyway, if you have a ticking noise it might be some of the rockers in the engine.

Just thought I drop that in, so people know.

Thanks for the reply.