Thanks again for replying. Yes i would agree that the older Monza is a nicer watch and in particular i prefer the dial layout on the Cal 12, to me the offsetting of the dials on the cal 15 isn't as pleasing. I'm learning more and more each passing day it seems...

So the black Heuer box the watch is advertised with (has white HEUER woding on it) isn;t the original, as it would have come with a helmet im to assume? (picture below)

It is baffling that the price is similar to a good condition TAG HEUER Monza (approx £1000) and it seems even the longer term HEUER collectors are unsure themelves as to why (especially considering rarity) therefore i think i shall purchase this one as you do not see many semi complete like this. It could prove both a good long term appreciator and a enjoyably wearable watch.