I have found that if you buy the seconds that Carpenter sells on ebay the lens and frame are not together. The tiny little posts on the lens that they place the aluminum frame on and melt them to hold the trim did not work. So that makes it much easier to get in there to mask and spray without the lens to be in the way. I just put some strip calk in a few place to hold in place for my 73 which is not painted. They are half price also which is great. They are not always on there. I got two sets when I ordered them and will be doing the others for my 72.
If I were you I would take them apart will be much easier to work with. There is not as much glue used on the repo and I see no reason to glue them anyway. They are held in place when the light is installed.
To make custom width masking tape I use a rotary scissors and cut to any width I need. It is much easier to mask the radius with narrow tape. Great when doing a console or dash panels also. You can get the cutting board with grid and rotary scissors at like Wal Mart in cloth section. They are usually used for making quilt patches.