I've restored marker light & tail light lenses to look like new. It's actually not very difficult, but quite time consuming. If you have an original set of lenses that you want to reuse, it might be worth it.
First you need to evaluate how deep some of the deepest scratches are. If they are really deep, start with 220 or 320 wet sandpaper & take a tiny piece about the size of your finger tip & see if that starts to remove the scratch. If it does, keep working it until you think the next higher grit will almost make it disappear.
When all the deep scratches are gone sand the entire lens with the next highest grit. Hopefully 600 or 800. Then continue sanding with 1000, then 1500 until you reach 2000 or 2500. By that time the lens should be really smooth, but really dull in color.
I have a buffing motor with various wheels & compounds. Plastics can be polished with either a loose wheel or a string wheel. The string wheel is preferred. Plastic heats up quick, so remember to use light to no pressure while the motor is spinning. If you aren't careful, you can melt & destroy the lens is less than a second. BTDT.
70 lenses are going to be tricky with the raised edges, so you'll have to use a Dremel & a tiny polishing attachment. To be honest, they will probably be challenging, but very doable if you're patient.
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