I'm using both the Main Support System and Oil Control system on my 331 from DSS. The MSS is made of T-6 6061 aluminum which is very strong, yet absorbs much of the engine harmonics which allows for a built 302 to withstand high horsepower applications. The cheaper steel versions do not have the same absorbing feature and are much cheaper (like $99 or so).
Both (MSS and oil control sys.) are very nice piece's from DSS, but will require some minor grinding in order for eveything to fit properly (regardless of what they tell you).
Hope this helps,
E