Would anyone know the answer to this.Using the Dart tall deck Big M,i have a Merlin marine air gap intake.It looks like the distributor mounting has been machined(recessed) down to accept standard height distributors.Would this be the case?

Yes, the manufacturers do countersink the dist. pad on tall deck intakes . Your can also use an adjustable slip collar MSD dist. to fine tune the height if needed.

mrhorsepower is correct, that is the set I am running, intake is countersunk, but I also used the msd with adj. slip collar.