drive train+axle help for triumph

[v8mini1]

hi there wonder if you guys could shed some light on a few things for me. my freind has a
triumph vitesse running a p6/sd1 3.5 LT77 boxx, 2.2 rover prop going into a quafie diff with roughly 3.7 ratio and uprated uj's running up pod currently 14seconds but the car has only 175's back wheels has hardly any traction. heres the thing im about to do this to a herald but like to change a few things aka (if any 1 has ever heard or seen and axles for the back end which wudnt change the look of the car dont mind midifying inside aslong as i dont have to altor the archers roughly 50-55 inchs from tyre to trye width) id also like to consdier diferent model number LT77 gearboxes maybe be quicker gears for 1/4mile, back axles would be the best thing to change , also any 1 no any place which wud make custom wheels like deeper dish so put fatter tyres on. so if any 1 has ever heard rumours,got any ideas,or has done it id love your imput. Also if any 1 is an engineer on here lend me your knoweledge on roughly price wise to shortend a jad axle set up, thanks guys