how complicated do you want it to be?
as for a quick history on the V300, espescially the UK market that's spot on. but it does miss out on quite a lot of facts,
this is (in Dutch) the story of how the V300 series was born
http://volvo300club.nl/berichten.php?co ... u=volvo300
and this is (in Dutch) the short version of the modeldevelopment, and still is far from complete to be 100% exact
http://volvo300club.nl/berichten.php?co ... u=volvo300
i'd leave it as it is wich is a nice introduction without making things too complicated.
as for the MK's, the simplest thing is to call everything with 343 or 345 on the back a MK1. roughly speaking there are 5 different versions of this MK1 and even more changes by half or whole modelyear so it's most sensible to call all those MK1 and divide them by modelyear for the main changes; here's a short example of those changes.
-MY76/77 pushbutton light switches, brown dash; short bumpers, amber gauges
-MY78 short bumpers, black dash with amber gauges
-MY79/80 licence plate is now bolted on the front bumper, new clockset (with green gauges)
-MY81: old nose style, bumpers are extended to the wheel arches
-MY82: mk2 style front, but old dashboard and interior
however, most of the time even that won't do as in detail there's too much that changed in the early years to make a sensible list that is easy for a newbie to follow.
MK2 for when the 340/360 series was introduced in MY83, so was the later style dashboard, new interior etc
MK3 for when the 340/360 got its last mayor facelift at MY86; new bumpers (with indicators in them) fully glued rear windscreen, new taillights etc..