If you are going to be doing on track driving then get a custon 4 point roll bar and not a Auto Power or Kirk bar. They bolt to the floor which is only thin sheet metal.
If you were to weld in three steel plates about 1/8 -3/16 thick in the corner of the floor where these roll bars bolt to them they may actually work in a roll over.
I bought a Mustang tback in 1995 hat had a Auto Power 6 pt. roll cage installed in it. The cage was first bolted in and then 4 of the mounting points were welded to the floor and "TO THE ROCKERS"!
I never liked the cage, it didn't give me that much room and it didn't stiffen the car that much. I kept it because I never could decide to make the car a full on race car before I decided to sell it.
SCCA allows you to use as much as 144 sq. inches of steel plate per mounting point on their roll cages intended for road racing cars.
"Drag racing is for those people who don't know how to down shift and brake at the same time. "
DD '12 VW Jetta TDI, Race car '87 ITA 16V Scriocco
Cars owned: '86 Mustang GT, '92 Mustang LX, '93 Mustang Cobra "R" #58