[Jack21]

On the street, generally, you need BOTH mechanical, AND vacuum.
On the track, only mechanical is needed.

For Hi Po engines, both mechanical and vacuum MUST be adjustable so each engine can be dialed in.

I'm running 14 deg static, 20 deg mechanical, and 8 deg vacuum. Like many of you, I have the MSD vacuum distributor, but had to replace the vacuum canister with the Accel unit. MSD in their marketing wisdom neither makes one, or offers advice on installing their competitors adjustable vacuum advance cannister.