wanted conversion kit from 460 to 463 !!!

Briefly, I don't think there is a place in the UK which will do this as part of their "regular" work, besides a Merc dealer, which isn't an option, unless you fancy paying more than your truck's worth in parts.
However that is not to say the bits and pieces are not obtainable. Over here and in other forums/pages (benzworld.com, pointedthree.com,gwagen.de,vinthers.dk, 4x4abc.com,clubgwagen.com, and more from browsing around) you'll find a lot of part numbers and procedures (and some costs). Some bits you can only get from MB or scrap yards, others are more generic.
The cosmetic changes are mainly:
front and rear bumpers and fog lights
side view mirrors (now they only need one hole for mounting, you'll have to fill up the other)
front grill (plastic instead of steel)
headlight surrounds (plastic instead of rubber)
rear lights (some minor bodywork mods needed, according to sources)
wheels (you'll need spacers for most 463 alloys, 4x4abc has an excellent page on factory MB wheels)
all indicator lenses are white instead of yellow, and the latest headlights are clear, so you could go and change those as well. the cheapest bits are the side repeaters, peanuts from www.orc.de but most everything else costs an arm and a leg, but it is very doable.

Fill in your profile so we can see where you are, there might be someone able to assist in your area, maybe a garage familiar with Gs?

Have fun on the forum...

M2