69 Barracuda Side Markers

I need to replace the side markers on my 69 Barracuda to re-register my car. I've done a lot of engine and drivetrain work on my car, but not too much on the body. Are these easy to replace? I got some replacements from Layson's, but they didn't come with any instructions. From the look of the replacements, they should just snap into the holders. Are there any tricks to make this easier? I re-painted my car about 6 months ago and don't want to mess up the paint job.
Thanks for your help.

Just checked the markers on my 9ner... they are attached from the back using a 'u' shaped bracket that measures slightly longer than the marker itself.

Two coarse self threading nuts per unit pulls the marker tight against the body inset.

Not sure if gaskets were ever used originally, (I know I don't have any), but if you're conerned about the paint... you could always make some up.

Personally, I don't think you need them.

They used gaskets. I had an NOS set I sold a year ago.