The tko with pro5 shifter is just fine on a 1989 Road going Sapphire . Would not be suitable for a race car I guess. Can I point out I don't use a tko600 . My tko box was built in the States by 'Dark Horse Performance' with gear ratios to suit the Cossie & take 700ft-lb. It cost more 16 years ago than a tko600 does now. Like my Diff it was fitted for strength not speed & its certainly been strong as neither have broken, gone wrong or until my latest build had its oil changed. THE ULTIMATE FIT & FORGET.