Hi MetisUlysses,
Congrats on making the decision to switch to the art history track. While I have no idea how likely it would be for you to get into a top 5 MA program, I am sure there is an MA program that you can find. While a top 5 MA certainly doesn't hurt a PhD application, I wouldn't say it is necessary for getting into a top 5-10 PhD program. Find a program that you think is a good fit, hopefully has some funding, and allows you to start making connections in the field. While in the MA, do your absolute best (of course) and consciously keep an eye on your CV so that you can flesh out all areas.
Best of luck to you.