2 ways to physciallt bolt the heads on, either change the PCD of the studs in the heads (weld them up and redrill holes) or change the PCD of the studs in the block (either with adaptor block or redrilling the case).
Once they're on, you'll need to have a set of camshafts made up by someone and work out if you're going to use chains or cambelts to drive them.
Then work out oil feeds to the heads and cam box assemblies, obviously one off manifolds and exhaust systems would be needed.. erm which bottom end would you use? The T1 case wouldn't really be up to the job unless you use a new ally case. Russ Fellows has done this on a T4 block and turbo'd it.
Go to
http://www.centralvwaudi.com/About.htm to see pics of it on the rolling road.
It makes over 300hp and is Turbo'd.
MG