There was some discussion of those a while back (I've got one on my bike).
See eg. viewtopic.php?f=4&t=4184&p=26011#p26011
There are several variations but they all basically use mini components to get a 2LS front brake - mine is certainly an improvement in the braking department although I do notice the extra weight in the front wheel (I've got a steel backplate - as originally used in the mini and probably the heaviest arrangement).
Can't say I've ever felt the need to convert the back brake though!
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)