Unfortunately, these holes are going to be difficult to fill.
That said, this looks like a much better vehicle than the previous one
If you have access to someone with TIG then it is reasonably easy to fill all surplus holes using scrap bits of Birmabright. You can make them disappear completely.
I agree with Tom that this is a good candidate for a restoration. I would get the unit numbers - engine, gearbox and axles and also the steering box and see whether they look right for the chassis no. but if they are right then there isn't much wrong with it.
It seems quite common to find early vehicles which have had a facelift at about 10-12yrs old to make them look 'modern'. The black panel and the padding around the dash fit with this, together with the black vinyl seats. Instruments and the steering wheel and horn bracket do turn up on Ebay. Not cheap but easy enough to find on the timescale this is likely to take. The most difficult bits to find would probably be the seats. Original elephant-hide seats are near impossible but the Exmoor Trim ones are a good substitute.
There are several variants of the heater vents, from different eras. Since heaters were an aftermarket option anyway I have never been quite so concerned about finding exactly the right ones - who knows what date someone added the heater. However, i agree with Tom that one of the various metal types would look better.
Basically, you would be budgeting a reasonable amount (maybe £1-2k if you wait for them to come up on Ebay?) just for parts to replace the currently fitted, perfectly serviceable but incorrect period ones, plus the seats on top of that.
Alec