Bit late in adding my 2p worth here but... In my personal experience, the Weber 34ICH is a decent enough carb. It's a plodder in that it does not stress the engine out in any way, fuel consumption is about what you'd expect from a standard 2.25 engine and speed is, well, depends what you drive but an ambulance (aerodynamic brick does about 50 to 55mph. I would like to fit something like an SU at some later date. Without even looking I'll need some sort of adaptor for the inlet manifold which, if I am lucky, will be no more than a steel plate. I don't know about linkages but it shouldn't be a problem... famous last words.
Now, 'Landy-Novice' is looking for a lot more power than the change to an SU carb will give (on its own). I'm sorry to say that you are on to a loser and possibly the beginning of a money pit if you seriously pursue this quest. The 2.25 petrol Land Rover engine is damn good long lasting torquey engine. It is what it is and that is a workhorse.
Now, having said that, I am quite sure it is indeed possible (with the right amount of money) to work on a 2.25 engine and get it doing 100mph possibly more. To do this you would have to strip the engine, balance everything that can be balanced, equalise various weights such as pistons, con rods and any other multiple reciprocating parts. You'd need the crank lightening (to go with the balancing) and hotter cam. There's gas flowing on the head and, if you really want that power it is possible to fit a supercharger. For that lot, unless you are really lucky and have free access to an automotive engineering shop, you are looking at a lot of money. This is all before you even look at uprated exhaust and carbs.
So, let's assume you've been able to do this. You have a quick series Land Rover that'll win you prizes at the traffic light grand prix You will almost certainly lose low down torque characteristics Worse than that, you have not even started to think about how this newly transformed beast is going to handle... It will need uprated brakes and suspension (don't forget the dampers), you may have to consider lowering various bits to get the centre of gravity down. Then, will your gearbox handle the extra power?
My advice, and yes I am a crusty (nearly 50 year) old fart but I was once a youngster after every ounce of speed I could get out of a vehicle whether it was car or bike, is accept the vehicle that you have now. Put your money into improving it for comfort and reliability. You say that you can weld, great. have you any papers to show that your skills have been professionally assessed? If not book yourself on a course at night school if you can. A qualified instructor can then point out any bad habits you've picked up and put you straight, we all have bad habits. This will be a great help to you in the future as you progress and could save you money. By all means grab a V8 if it comes along. Get yourself an engine stand and set the engine up to run on that. Learn how it responds to various tuning tricks and then perhaps think about swapping it out for your present 2.25. To be honest, I think you'd be better going down the Tdi route though but it's your vehicle
If you have a good, solid and reliable workhorse you have something to be able to pick up bits and pieces. Those bits and pieces could be the basis of another Land Rover that you build up as a hybrid with more power; a plaything. Or, it could be a cheap little hot hatch which is again a plaything. Above all else be careful and learn safely the skills you need for driving.
