do i need to run a slip collar on a msd dist the motors are on there first rebuild.didnt maching the intake.and the dart heads are brand new. thanks

Maybe not. Remove the dist and take off all the gaskets. Now reinstall the dist. With any luck, you will have a gap between the dist base and top of the manifold. If so, you can add the necessary gasket(s) or shim to get the right fit. Someone else might be able to tell you how many thousands (.000) above all the way seated your dist should be. It the dist doesn't bottom out (dist too short), you would still have the option to mill in intake at the dist and still use your current dist.

Best to measure down to the oil holes in the block and see if the orings line up properly. Then look for any other interference problems.
I had a super tall deck with sheet metal intake. The super tall deck MSD dist was too high.
I put a short deck dist in the lathe and cut off the ring. Bought a slip collar and did some measuring. Fit on that block and now on my tall deck with regular intake. Thats the easiest way to get it where it should be.
Hope that helps.
Dick