The first thing you need to flat tow your 1990 Mazda Miata is a base plate kit. Which for that you'd want the Roadmaster part # 711-4 which is a confirmed fit.
In addition to the base plates, you will also need a compatible tow bar, safety cables, lighting, and supplemental braking to flat tow your vehicle. The most popular compatible tow bar is the Falcon All Terrain, # RM-522. This has non-binding arms which makes the setup very easy to connect/disconnect.
For lighting/safety cables,... view full answer...
I have a solution for you. Unfortunately, we do not have a hitch form your 99 Mazda Miata.
The best option would be to use a trunk mounted bike rack like the Saris Bones 2 Bike Carrier, # SA805BL. The Saris bike rack is confirmed to fit the trunk area of the 1999 Mazda Miata. This carrier has a 2 bike capacity with 35 lbs per bike. view full answer...
I have a solution for you. The Curt Class I Trailer Hitch Receiver, # C11729, is confirmed to fit the 1996 Mazda Miata. This Curt hitch has the typical horizontal receiver tube that will use the a standard ball mount or mount a hitch accessory without using an adapter.
This Curt hitch has a tongue weight rating of 200 lbs and has the 1-1/4 x 1-1/4 hitch receiver opening.
If you are planning to use this hitch for an accessory like bike rack, then Curt requires the use of a stabilizer strap... view full answer...
What you will need to use your Blue Ox Rangefinder II with Roadmaster Base Plates, # 711-2, is the Blue Ox Rangefinder II to Roadmaster Bracket Adapter, # RM-037. This adapter will attach to the Roadmaster base plates and then to your Rangefinder tow bar to tow your 1999 Mazda Miata. view full answer...