Yea, they modify both. They send a whole new tensioner and 'roller' .. Much better bearings than the ATI unit, which I replaced the bearings in twice in less than 5000 miles..

 

My ATI kit is quite a few years old now, but the old tensioner that came with my D1 was not spring loaded. After you put the belt on, you had to tighten down a nut/bolt combo on the tensioner and it pretty much became a static tensioner ..

I don't have any of the original stuff, I sent everything to SD and told them to throw out what I dont' need

I've been extremely impressed with the people up at SD Concepts. I am yet to fully test the system, but their customer service and time they took on the phone with me was outstanding. If you do a search in this forum, you'll find a lot of stuff on their tensioner and the Big Block Chevy Hub/Snout thing which they also helped me with.

--Sean