Hi Ian I have been running a 3.8 mark 2 for twenty plus years now and 15 years ago changed the uprights to 420 types with three pot calipers
I exchanged some old ones at Jayar motor factors and for £85 each they rebuilt them as new
A new set of pads which are a lot bigger than the mark 2 square pads was fitted and I have changed them once at 20,000 miles. On the MOT rollers the brakes were perfect and even the self adjusting handbrake worked with standard calipers.
Having driven replica SS100’s with 4 pot brakes in the wet there was no hesitation in locking the front wheels which was a bit frightening. End of the day its your choice and money!
Cheers
Brian
I stuck with the standard calipers in the end , and fitted EBC Green stuff pads .
more then happy with the performance .
Now sold off all the other parts , happy days 
I converted to Zeus front and rear. Very little improvement for my 3.8 Mk2. I have another set to change for another car but when the time comes think I’ll recondition some 420 calipers I already have despite owning a further new set of Zeus bought a few years ago. I’ve found that with normal driving the standard brakes are good enough, I just happen to have the 420 brakes and might as well use them.
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