Ive had a reply from veedubdude!
Right, Ive learnt alot since I started, and Ill try and get the basics over.
The 1.4, and 1.6 engines are basically exactly the same. The thing that increases the 1.4 up to the 1.6 is the crank, rods, and pistons. However - (Ive found this out since I first started the build) it is not possible to swap them over onto the 1.4 block. The
problem being the 1.4 block is aluminium; (Im yet to come across a 1.4 block that isnt the aluminium one) and hence once the crank bolts are loosened, the whole block actually distorts, which means the tolerances for the shells arent correct, which means rapid engine wear and failure. A couple of people have questioned this, but check out any haynes manual, or if you have access to it VW's own ELSA programme, and it is clearly stated. You cant even order parts for any of the short block engine from VW except for the 1.6 16V GTi engines (as found in the lupo and polo GTi's).
Which is one of the reasons I rebuilt my engine again onto the lupo GTi block when I found out this information - plus the fact the 1.6 16V GTi engine is built onto a cast iron block which is stronger.
All the heads are the same, valves, roller rockers etc throughout the range, so you can use what you already have. Only difference is the cams used throughout the range. The standard 1.4 16V 75bhp cams have never been run on a GTi block, so I dont know what the outcome would be... Ive personally gone for the cams out of the 1.4 16V 100bhp lupo sport engine; so will have results as to how they do when I finally get her all mapped up on the rolling road!
So my advice would be to swap the short engine over - only thing that needs changing is the flywheel. You just need the flywheel and clutch from your original engine so that it interfaces with your gearbox correctly. The 1.4 flywheel is actually lighter than the 1.6, so this acts as a free mod! The only
problem si technically the 1.4 engine redline at 6k RPM, whereas the lupo GTi redlines at 7k RPM. Personally I dont see this being a
problem, but its something you should be aware of.
The lupo boys have had the GTi's remapped up to 8k RPM with no
problem, which is what I intend to do too, as there seems to be no problems with this.
Next is the air intake - if you have the plastic inlet manifold Id suggest changing it over for the lupo/polo GTi metal one, plus injectors, fuel rail, and TB. These should be plug and play. Only thing I found was that I had to splice into some coolant pipes for the new TB as it needs cooling.
In terms of mapping the engine, you will have to check what ECu you have got. Ive had two different sources of information - stealth racing have said the magnetti marelli ECU needs a chip replaced before it can be mapped, whereas the bosach ECu can be mapped up straight away. (I think thats the right way round, Ill have to check for you) ********* have said they can map both it doesnt matter... NOw the bosch and magnetti marelli where both used ont he 1.4 and 1.6s depending on year of manufacture, so thats something you'll have to find out for yourself.
Finally - the weakest link is going to be your gearbox. I dont know what the gearbox is like on the seat 1.4/1.6s but the golf mk4 1.4/1.6s have an inherent
problem with the crown wheel in the dif being held on with rivets. These break regularly with 75bhp, so with double that and more I cant see the gearbox lasting too long... Good news, the rivet fix kit should cure this if the worst does happen (replaces rivets with bolts) and then work fine, however a recon box will set you back around the £500 mark...
Hope thats of
help, anymore info you need just ask!
can be done if u have the money 
