Many of the Converters used cheeper after market rear H/AC units. The factory units often did not suit the layout of the conversion (larger & longer windows for example.)
Many Converters got out of the bussiness in the early 90's due to liability issues. Finding replacement interior items for those vans can be very difficult.
Have had several and ofter found it cheaper to have a new unit installed than to repair a broken one. Example was a broken Captains chair to remove/replace with an identical would have cost more than replacing both with new after market chairs.