'RHOM' Star Julia Lemigova Selling 1966 Ford Mustang Fastback

Julia Lemigova is trading in the horsepower in her classic Mustang for goat power ... and one lucky buyer -- with a whole lot of cash -- can benefit from a sweet new ride.

"The Real Housewives of Miami" star is selling her vintage 1966 Ford Mustang 2+2 Fastback ... a car decked out in gorgeous maroon paint with a heck of a lot of features and just 12,486 miles on it.

The car's got a 289 V8 engine, vintage air conditioning, custom aluminum wheels -- that look just like the OGs -- and a custom grill, parchment pony interior, wood steering wheel, retro sound custom stereo and fold-down rear seat ... talk about a blast from the past!

Of course, another major selling point is its previous owner ... JL's got the car up for $42,500, and she doesn't really wanna part with it -- but she tells TMZ she needs the space for hay and animal food now that her goat, Elvis, is staying with her a few nights a week.

Julia tells us she loved the idea of riding around South Beach with her wife, tennis legend Martina Navratilova, in the passenger seat ... but found she's more of a pickup truck girl instead.

Not only is she not getting enough miles out of it, but Lemigova says it's taking up space -- space she needs to store Elvis' hay and animal food since he's staying with the couple a few nights a week now ... he used to stay full-time at their farm but apparently he's more of a house goat now.

Don't worry animal lovers ... JL and MN have arranged temporary accommodations for their happy friends while they unload the car -- so he's not out wandering the streets of Miami.

Potential owners beware -- the car's got a manual transmission which Julia tells us she learned to drive while still living in Europe -- so you'd better know how to drive a stick!!!