Yea I agree what blu says p60 is the best bet to start with but see if you can pick up a full sporting,maybe an mot failure or one with the headgasket gone, I was just saying that by doing it by collecting parts will end up costing a fortune, however splitting the cost of buying parts does make it a lot easier and by god its a good feeling once you've upgraded
Its not as simple as changing the engine though u will need (off the top of my head
Sporting Gearbox
Sporting driveshafts
Sporting gear selector box
Sporting engine mounts
Sporting speedo cable/drive
Sporting clutch cable
Sporting exhaust manifold
P60 engine
Wire and connectors to extend the parts of the engine loom for the new engine
Plus all the rebuild parts that you may aswell get whilst ur at it
Headgasket set
Clutch kit
Cambelt kit
Water pump
Fresh oil filter
Induction kit of some description
Then there's the fluids
Gearbox oil
Engine oil
Coolant
You may aswell replace the brake fluid at the same time
In my opinion ( and many will disagree) the 899 brakes are more than up to the job of stopping the p60 upgrade mine was running stock brakes and steelies and it stopped just as well as it did with the 899
Sorry for the essay but there just a few things to consider when doing the engine conversion and aren't cheap to buy even from a scrappy
Its do-able but u really are better off starting with either a sporting or buying a worse for wear sporting to strip for all the parts you will need
Lee