It's one of those cases of why build what you can buy! However if you have plenty of time on your hands then why not!

Not done it myself but from what i have picked up it will be a big job. You are looking at engine and associated bits, loom, Front and rear ARB's, Rear beam for the rear disks, suspension to cope with the heavier engine, front disks (bigger on the 16v i think), clocks and perhaps more!
To top all that off you will have to insure it as a modified car which may cost you more!