Where the slot in that drive goes is dependent on the distributor. MSD's have been known in some engines to be miles off with rotor direction/#1 tower when the drive is installed per the manual.

I usually identify where I want the #1 tower on distributor, figure out where the tang is pointing, get drive dropped in. Then when ready to fire it up and wired, hook up a timing light on #1 wire, timing mark in 15-20 BTDC area. On a BB turn housing counter clockwise, turn on ign, and twist housing slowly back clockwise watching for the flash. Should be very close to timed up.