ALl I can advise is that noramly they might have been 30 thou and on LPG I recomend 27 thou.
Or fit Iridium plugs, they are damn good but pricey.
As for the rims I'm pretty sure there are 16 inch rims out there in Disco II fitment, that sounds like what you are asking. Perhaps some P38 Rangie alloys would do the job and they can be had for peanuts because no body wants them at the moment.