Those ebay ones I bought really went in nice, I mean right in! I've even had non-LEDs be a bit tough to go in on various sockets, likely because the 'recipe' has changed some over the yrs, meaning chinese bulbs are a slightly different size, lol. (eye roll)
But honestly I can't remember what the base contacts were shaped like, if that still matters knowing that they fit my same year car. I think you'll be pleasantly surprised at the brightness difference too! I will have to get wifey to hold the brakes on, while I click off a pic --in broad daylight, and then report back here. We have a car show tomorrow, so it could be real soon!
Oh, btw ....2 ten or so mile cruises in the past week, and no one has yelled out at me from a neighboring car, haha.
I'm also researching 3rd brake lights, but still looking ......don't like a lot of what I see out there, but if the LEDs helps me, I can bid my time on the 3rd one.
Is the bottom of the bulbs you used the 'normal' 2 round 'dots' so to speak? The pics don't show but the single on ebay but they are showing dimensions so a stock photo is probably used.