LED replacement bulbs

Hi all, I've done a search here and can't seem to find the answer I'm looking for. I have a '66 Barracuda and want to install some LED bulbs for the backup lights and lower taillights. On a side note, even the factory parts book and owners manual doesn't show which bulb is used for the lower taillights! I'm assuming it's the same 1073 as the backup lights, but, I may be totally wrong! Anyway, I see a 7506 LED bulb is supposed to be the replacement for the backup lights. The potential problem I see is the length of the bulb. This model has historic problems with melting the lenses on the taillights because of how close the bulb is to the plastic lenses. I'd like to use a short bulb (like a license plate bulb) but, I don't see one listed that is that short. I guess I will try the 7506's, but, a couple of questions. What sort of heat does this bulb produce? Hopefully less than the incandescent one it replaces. One version is slightly longer than the 1073, so, that is a concern. Also, Sylvania says it's not street legal....what the heck is the deal there? Just hasn't been fully tested yet to get the DOT approval? The specs on the bulbs don't compare apples to apples in some cases. Some bulb use watts, some use lumens, some also list color temp in Kelvin. That makes it hard to compare when it comes to light output and heat generated. I'm basically trying to get a brighter light without adding heat to the lens. Otherwise, I'll just use the stock incandescent bulbs. Any suggestions?