Take or send your heater to Ark mirvis,  31 Byram Bay Rd, Hopatcong, NJ,
201-398-6363- he is a genuine German Ebersbacher trained techician- prowls
the flea Markest all the time for heater/parts- says he's amazed how many
are sold with vital parts missing, and these heaters need the failsafe
devices they come with so you don't immolate your bus with raw gas or an
explosion.  I had one in my 71 bus in the spare battery location on left.
You could keep spare battery under seat.   You need a t in the gas line
BEFORE the fuel pump to run to the heater, and cut a hole in the floor of
the body shelf to run the exhaust pipe out.  The line for heat output runs
in the free space left of the gas tank and under your rear bench seat.
Good luck- gave good heat; stick a flexible pip;e in the output end and dry
your hair with it!       MB in NJ