factory svo on ebay

Correct. SVO is Special Vehicle Operations. The Mustang SVO was produced in 1984, 1985, and 1986 only with a grand total of about 9000 produced. They were all equipped with the 2.3L turbo I4 engine. Early SVOs produced 175hp. Later, they were 200hp. They were all equipped with a T5 manual with "Hurst designed shifter." The suspension was slightly altered with different front control arms and a different shock configuration in the rear. They were all 5 lug, 4 wheel disc brake from the factory as well. If there is any other info on the SVO you want, let me know. I have quite a few good information sources on them.

You can, however, the SVO is 5 lug, and also parts are very very rare. My suggestion to you if you want 4 wheel disc is find a junked thunderbird turbocoupe (1987 or 1988). They have a rear disc brake setup and are 4 lug to match your fronts. The turbocoupe rears are a lot more common and can be found fairly easily at a salvage yard. If you do go to a 4 wheel disc setup, you will also have to change out your proportioning valve. You can get nice aftermarket adjustable valves so that's no biggie.