Driveshaft Swap?

[GLIDEHM]

I have an 84 300d with an auto trans. I have been experiencing some driveshaft vibration after i changed the flex plates and the center carrier bearing. The two halfs were seperated after they were marked in order to ease removal, but unfortunately, during the reinstall process I wiped off my paint marks and was unable to know if I got the two halfs back together properly. Since changing the parts I have been experiencing a pulsating vibration from 40-55mph and asssume that the shaft is no longer balanced correctly. I have read in some of the other threads that the slip yoke might also be a possible culprit? Any ideas? I believe that the previous threads mentioned loosening the slip yoke nut and cycling the rear suspension to get it positioned correctly. Anyway, does anyone know what years and models interchange with my driveshaft? Obviously it will need to be an auto, but I was wondering if numerous years and models (240 & 300) have the same length shaft. Knowing this would make finding the correct used part in the scrap yard alot easier. Thanks for the help!

GLIDEHM