I just installed a 8pt S&W in my 91GT. It was a lot of work but it looks great, to put the 10pt in it is best to remove the dash so that you can weld in the knee bar properly. I also think you loose the heater core with a 10pt, due to where the bar comes down through the dash. If you can get rid of your rear seat I would suggest the X brace to the shock towers it offers a lot of support to the Fox Bodies and was strongly recommend by Accufab Racecars in Baltimore.
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Check Out My Site 91GT,Holley SysteMAX II Kit-Heads 2.02" x 1.60" port matched to a 1262,Anderson N-61,24#,76mm C&L,Full MAC exhaust 1-5/8" Long tubes,2-1/2" O.R H-Pipe,2 1/2" cat back, No A/C or PS or emissions, 12" K&N Filter,RNH PERFORMANCE Ram Air,Ron Davis Radiator,Full Suspension,S&W 8pt "X" brace,JAZ seats,3:73's,Welds..etc,4:30's and 31 splines coming very soon!