You didn't mention whether this was an auto or 4speed...here's my point. I had a similar problem with my Travelette. I put in a 392 that I had rebuilt and had in a Scout for 5 years. It always ran smoooth!!! When I installed it in the Travelette, I had a vibration that I couldn't track down. I got to thinking...what was the last thing I changed; it was the clutch and pressure plate. I remembered that I purchased a Brute Power (I do NOT recommend) clutch and pressure plate and when assembling them I noticed that the holes for the pressure plate were elongated so that it would work on an 11 or 12 inch drilled flywheel. Since I had planned to convert to 5 speed OD, I pulled the tranny and clutch assembly. I had a freshly resurfaced flywheel on my bench that I placed the pressure plate on and loosely screwed in all the bolts. You guessed it...I could move the pressure plate in all direction about 1/16 of an inch. There was no way to get it absolutely centered. I called the company and after arguing with them several times, they would not stand by there product but instead told me it was a "universal" fit!!! I ended up trashing it and sent a used pressure plate and clutch to have rebuilt. After installation, there was NO MORE VIBRATION! Moral of the story...the vibration my not be the engine at all. Contact the previous owner and ask if they replaced the clutch if the Scout is a standard shift. If so, this possibly may be the problem.