You cant use 16v clocks, the g60/rallye ones are specific as they have to handle boost. You can however swap the speedo or even just the dial face though, as long as the max. speed matches up. You'll want to keep the original speedo so you can convert it back to original when(if!!) you ever sell it

RHD/LHD lights are fitted to all Rallye models

Arches & Sills are a weak point on these cars, apart from that its a MK2 with all the usal MK2 problem areas. Other than that, find out when the charger was last serviced, check the AWD system for any obvious problems as well as the exhaust. Both items are Rallye/G60 specific and not cheap to replace!