The Holiday and Coleman stoves were ubiquitous in this era of trailer. If the guts to the oven are missing, I'd suggest to shop the RV junkyards for a working unit. The stove/oven combo slides into position and is held by a few screws on top, towards the back. REpairing these older stoves can be difficult as the thermostats tend to be mercury filled and are no longer available. That, and the standing pilot light (also problematic in an oven) beg for a more modern replacement.
FWIW, my oven doesn't work, at present. I will try to repair it but chances are that I'll have to make a choice---live without oven or get a replacement.
Good luck with your rig, it is cute as a bug and I'm sure you will be seeing a lot of interest at the campgrounds.