There is a basic formula you can try. I am assuming it is a standard, free standing greenhouse.
Your shortest pieces of aluminum should be the side ribs. There should be 4 corner ribs made to accommodate glass or plexiglas in two directions.
Heavier pieces of aluminum rib should be the roof pieces. There should be triangles inside which are to brace the roof to the side walls.
The bottom pieces made to run the 6' x 6' shape or the 6' x 10' shape might be the heaviest pieces, thickest metal, bent oddly in order to sit atop a wooden foundation like 2 x 8 or 2 x 10 lumber sitting vertical on edge.
If you erect a 6 x 10 solid and SQUARE foundation, that might be the first thing to do. Using treated lumber of course.
I seriously doubt you'll find the exact instructions after 36 years. Are you sure that you didn't take it out of the packing and bring it inside when you had the intention to build it. Then maybe change your mind and got side tracked?
