Does the stock intake normally vibrate?
 

I put my stock intake back in my '85 today because I will be doing a lot of hwy driving in the near future and I would like the quieter ride. I got new rubber mounts for it, but when I start the engine (which is running relatively smooth after valves and timing) the intake is vibrating violently at idle. I will be surprised if the mounts last more than a week. Is this normal?

I guess you're talking about the air filter housing? Check the bracket that the three mounts attach to - mine was broken that seems to be a common problem.

Yes, broken bracket.

Place a piece of rubber radiator hose between the filter housing and valve cover.

My mount was cracked too this morning before install. I welded it up and checked all the bolts. It was solid prior to install. I will check it again in the morning then.