I'm lowering the front of my 95 mustang gt, I'm replacing the the struts also, I read that I should replace the casters. Here's my question, I saw online they have 3 and 4 bolt styles. Why is there 2 different kinds?
you mean caster/camber plates?
You only need to replace the CC plates if the car can't be aligned other wise. the limit is usually around 1.5" drop. but that's not written in stone.
4 bolts are stronger. And IMO look better too.
Maximum Motorsports has a good write up on their website on why you should want the 4 bolt style (Cliff's Notes: it's a lot stronger and encapsulates the strut between the bolts, whereas the 3 bolt style doesn't do this and thus could bend/is not as strong). Drilling the extra hole really isn't that bad at all, just make sure you have a sharp drill bit. My suggestion is go with a 4 bolt style and don't look back.