Slant Six distributor question

I converted the wife's valiant to HEI and used a Mopar electronic distributor. The mount for the distributor is slotted where it mates with the engine and it is also slotted where it mounts to distributor. Question where the mount mates to the distributor, which is slotted, how do you set that, is it part of the total timing or is set and you set timing with it locked down any place??