First of all welcome to the forum. There is a how to section in the forum which gives you all the info on fitting a servo brace. One thing to remember is that you can't compare the brake performance of the F and TF with modern day cars . All the brace does is take the flex out of the bulkhead where the servo is bolted . If you get someone to press the pedal repeatedly and observe the amount of flex on the bulkhead where the servo is bolted it really is quite alarming. The brace just makes the pedal feel harder. Further improvements will be to fit armoured flexi hoses and better quality brake pads and of course change the fluid. Fitting the bigger AP brake set up would cost more but would give the performance of current day cars . My TF is a 135 with a standard brake set up plus the brace and its fine as I'm used to it . You have to remember that MG /Rover had to scrat around the parts bins when building the F and TF and fitted Metro brakes to the front and I believe Rover 600 brakes to the rear on the small brake set up as they had to build on the cheap . They are still great cars so enjoy .
http://www.the-t-bar.com/forum/22-cjj-s-guides/75834-brake-servo-flex-fix
Servo brace