He was the drummer of 'The Escorts' and the original drummer of 'The Allman Joys'.
Duane Allman and Maynard Portwood during 'The Escorts' days
In Phoenix, AZ Maynard Portwood became the drummer of 'The Belanger Brothers':
http://www.localbandnetwork.com/Venues/venuedetail.cfm?VenueID=692
'The Belanger Brothers'
left to right: Gar Belanger, Johnny Q, Kenny Belanger, Maynard Portwood
Maynard Portwood (on the left) with 'The Belanger Brothers' manager Frank Ward
In 2016 Maynard was honored as a Vietnam veteran at the 'National Memorial Cemetery of Arizona in Phoenix, AZ:
https://www.findagrave.com/memorial/160291085/vernon-charles-portwood
(Thanks to Kenny Belanger for the additional information)