ive got a s3 88 and its slitty diesel the now but quite slow and i fancy either a v8 or 200tdi just to make hills easier

what mpg do you get out of the v8 driven sensibly? and what v8 is the best out of the rover selection? and what manual box goes on the v8?
thanks in advance
Not sure what has or hasn't been covered so far.
In short a V8 conversion on a Series is pretty easy. A 3.5 carb will give you heft HP increase and a lot more torque for similar mpg to the 2.25 petrol.
It's not quite a direct bolt in, but not a million miles away in terms of engine swaps.
A 200Tdi will also swap in with similar ease and can also be mated to the Series gearbox. The main advantages are better mpg and not phased so much by water. Fitting the turbo in and intercooler can be done behind a Series front panel, although swapping to a Defender style front panel and bonnet will give loads of room. A good Tdi is a pretty good match up to a stock 3.5 and arguably better in some regards.
Down sides, Series axles and diffs are pretty naff, so if you off road, esp with bigger tyres expect to break more stuff more often.
Series gearboxes are also a weak point, so again, these can potentially be an issue.
And you'll seriously want to look at improving the Series brakes and possibly suspension.
300Tdi can be done, but it's more work due to it normally using a different bellhousing and output shaft.
You could swap in a 4 speeder LT95 as an option, although bits are less easy to get hold of these days.
Or even an LT-77 5 speeder, but this makes the transmission longer, so you'll need a custom rear prob and might have some binding issues.
It all really depends what you want to do with the Landy though and why.
If it's road use only, then a 2.0 litre Rover T Series lump as used in the MPi Disco might be worth a look. Same power as a stock 3.5 V8, but more revy and car like, EFI and should offer up better mpg.