1960s Sylvania Color TV: My first all tube color TV

[Electronic M]

For chassis removal I forget if the D12 was this way(I think so but it's been like 5 years since I had mine apart), but the D16 definitely is....On Sylvania sets of that era the chassis slides into 2 side rails and locks to those rails with 2 rear facing screws. Remove the screws and unplug all wires and the chassis just slides out the back.

I've never worked on 80s inline sets or seen what you describe. Delta gun sets like this Sylvania don't care about orientation* and replacements were shipped face down.
*In service they would sometimes need purity adjustment and or degauss when moved from facing north-south to east-west but no permanent issues otherwise.