Ok, I just got in from working on the car since 9 am (now almost 830 pm) I think part of the problem has been I fell into a hole I helped create. We started this morning by putting car on a drive on lift and then taking the aux jack and raised the rear wheels off the platform (a safety cable included). We had been reluctant to do this previously but we ran the RPM up and down from 700-2000, in OD, Drive, etc. Along with working on the vibration issue I have been doing some other small jobs where problems were detected.. One of those issues was a tire just slightly getting into the inside of the rear fender well.. I dislike wheel spacers but I bought a pair of 1 inch and installed them last week along with working on the vibration I have had since building the car. So I continued to work on the vibration issue with many angle changes and nothing seemed to change, good or bad. So back to today, we are running the car up to 70 MPH on the lift, I am under listening and "feeling " everything I can touch. The driveshaft is humming along smooth as glass but at 60 the car is vibrating wildly. One wheel (rear driver side) is going NUTS. So to try to shorten this story I will skip the stupid things we did and just say we switched wheels and spacers side to side.. The wild vibration followed the drivers side wheel and spacer over to the passenger side. LIGHT BULB!!! So I removed the spacer on that side and remounted the wheel and no vibration at 60. So it appears along with driveshaft vibration I already had, we added more vibration from the wheel spacer. What can be wrong with a wheel spacer, I have no clue, will examine more tomorrow. I think this might help my 60 MPH vibration but I still have the low speed shutter which maybe now I can evaluate better that I have removed the self inflicted issue.. While under the car there is a noise coming from the rear end that I do not like so tomorrow I will be removing the 355 and installing the original 323. After completing that we will take another spin on the lift and see how the noise and vibration has been affected. In any case I will be back to troubleshooting the original problem. I think this wheel spacer issue has masked all the possible good things I have done in the last couple weeks so it is like starting over again,,, again!!.. Every suggestion has been written down and will be executed in the coming week assuming I get mostly positive results tomorrow. Along with the fact I have previously had 3 sets of wheels on the car, while running it on the lift today I was able to observe one of my wheels is less than perfect. I put it on the spin balancer and it was fine but when mounted it is not running very true. So that is todays efforts. All suggests, comments are greatly appreciated and will become part of my evaluation. Thanks to everyone..