While it is possible that Martin might have shipped an instrument with an oversized pickguard as a special order, a pickguard of that size and shape...
It is likely that the pickguard is indeed a replacement.
The Martin history books do not make mention of any instruments specifically made for Dyer....
I started teaching music about 1990. I've been performing on and off since 1979. I play most string instruments, with guitar, mandolin, and bass at the top of the list.
I accompanied Norman Blake on his record "Flower From the Fields of Alabama," and was a member of the Fletcher Bright Fiddle Band.
I work on just about all string instruments. My specialty is precision fretwork.
Location:
Southeast Tennessee
Occupation:
Teacher, part time luthier, semi-retired professional musician