Wow!   Looking good!!
 
I had a stock GM rubber mount and custom bracket to the 998 in the Hornet.  Not sure if a vibration is the right description, but could definitely "feel" the drivetrain more with some noise tranmitted through to the body.  I've got a GM-style urethane mount for my Javelin, 'cause my aftermarket AMC one is split ... again ... but haven't put it in yet.  The urethane is a little stiffer than the rubber one.  The stock GM rubber mount is much more rigid than the mushy AMC mount, so doesn't seem to absorb vibrations as well.  If you have your AMC mount, and it still fits OK, could swap it in to check?   If you have the 1 7/8" Super Comps, check that there's clearance to the driver's side engine mount and to the passenger's side strut rod bracket and the frame.  Mine are really close (had to trim the engine mount and tweak the headers to clear the frame and strut rod bracket).  Makes a significant vibration if it touches.
 
Hope this helps, RD.

Looks just BITCHEN at night!!! Def enough to make folks turn their heads and wonder what they saw Darn near like the Johnny Cash album "Mean as Hell" SH

I took a couple videos today at different times of the day so you guys can see the difference in colour between night and day . It sounds like it's got a misfire now so I'm gonna have to find out what's causing the popping sound .
 
Here's a daytime video
 

 
The sun going down  
 

 
Night video
 

 
What do you guys think , is it a misfire or something blown inside the 15 yr old mufflers ?
 
Paul

That car is Bad A$$ no matter what time of day it is! Nighttime has that effect though...Tom

I'm beginning to get the idea that you like the sound of that car idleing.
 
Dave Z

I tried running the car on Saturday without the p/s belt and with no change in vibration I ran the motor with the alt belt off too so no belt driven accessories were turning . The vibration is coming from the motor . I'm gonna call the machine shop that balanced my motor tomorrow . I might even drive the car over to his shop and let him see for himself . I'm hoping I can just put my stock damper on it and the vibration will be gone    . If that doesn't correct the problem , the motor is coming out . I'll tear it apart and bring the parts back to the machine shop and have him balance it again   . It's not gonna be fun doing this and I'm hoping he can get it balanced right away so I can put it back in my car in a week or so . This is getting so frustrating !
 
Paul

That sucks Paul.  Have you cut open an oil filter recently?