The typical 1300 or 4500 Trillium
furnace from the 1970s was a Duo Therm brand "gravity" (no fan but vented to the outside) propane
furnace. They are a 6xxxxx model number (don't have it to hand). I think the early 80's models started to go to the forced air (fan) models.
The 1300s had the furnace in the cupboard under the kitchen - all the way to the left by the bed. I think most of the 4500s (all? not sure if some had it on the kitchen side) had the same furnace but it was in the bottom of the closet on the door side. There should be a molded "flat spot" on the outside of the 4500 where the exhaust grille would be.
Here's a photo in the grille of my former 1300:
These aren't made anymore, unfortunately.