I believe it’s a model of a PFE wood express reefer. If it is the door opening is 5’ wide and 6’- 1/2" tall. That is a pretty typical door size. So, worst case is you duck your head passing through.
REA had about a zillion express reefers. Door width was either 4’ or 5’. Height ranged from 5’-8 1/2" to 6’-5"
Bigger door = bigger loss of cold air. Wooden iced reefers generally had small doors which could be sealed tightly, to keep as much of the cold air in as possible.
Not sure if the MDC car was based on a specific car, but many railroads had very similar express reefers in the 1910’s - 1950’s period.