Side marker "lenses", what's the deal?

[dmjlambert]

I would like to ask for some guidance about my 69 CST/10 please. My goals is to get the truck mechanically sound but leave the outside as-is as much as practical (for now).

For the Texas state inspection, a mechanic who does inspections let me know all reflectors must be crack free to pass inspection, and he pointed out that mine are deteriorated and cracked with age.

When I look them up to buy some, they are called side marker lenses. I was wondering why they are called lenses instead of reflectors, so I took them off. The front one came off in 2 pieces and the inside of the holder looks like it has an indentation. The back one came off all in one piece with the holder.

What is the deal here? Are the lenses used whether or not there are lamps behind them? I'm confused by what I see offered online for replacements, because some come with a holder that has a cross-shaped hole in the back, but there is nothing that looks like it would hold a light bulb. Mine just has a round plastic surface, no hole. I also find some that look like 2 horizontal bars, with or without chrome trim, and those are quite different from what I have. So, I don't know what exactly to get. I don't know if I want to light these up, I don't have wiring that goes to the holes where they mount. At this point I would just like the truck to pass inspection so I can get it registered.

If I did get the whole assembly with the cross shaped hole, and I wanted to add a lamp to it, what sort of holder would hold itself in that cross-shaped hole? If I started out with unlit markers, would I just cover up the hole to keep water, dirt, and bugs out? Example of new one I see offered is the last picture I posted below.