I have the same 80's vintage stove, bought it new back then.
that L shaped curved hollow casting is just for wood burning, it goes on the left bottom with a bolt I think.
the other 2 mystery pieces are needed for coal burning.
The long flat casting is the top baffle , the only baffle that is removable, and it allows vac-ing out the 2 lower baffles that are cast into the stove's rear casting and the slanted fireback. You have to place the removable baffle down through the oval exhaust casting with the damper in the closed position . It sits on 2 lips or shoulders cast into the stove read wall and the fire back.. It goes to the far left as you peek down thru the oval exhaust, right up next to the stove left hand side. Only goes one way, with the top being the flat side.
Now that small squarish casting with the small angle and slots, is the cover for the exhaust port, on the lower right of the fire back, below the grates. the small angle goes on the right, butting to the right hand insert casting, under a bolt, and is glued to both surfaces with stove cement. Mine has a other hole in it, and looks a bit different from yours, but it has to cover the rectangular opening that is used when wood burning.
You have the grated mounted correctly, but I would use a tube of stove cement in a caulking gun to glue the left hand and right hand parts to the stoves side. Just wet the mating surfaces with a wet sponge just before squirting the cement onto the removable pieces, and add more and smooth out with a finger to smooth the joints out.
I thought I posted a picture of that will check
Also search for my posts on adding a thick gasket to the doors as they almost touch the front grate--- that makes the stove really perform as no air bypass the fire box, make the stove more responsive
Ley me look around for those pictures, or I'll post some new ones