I have a 91 A6 block with a 97 Y8 VTEC head and love it!
However if you are gonna boost make sure you go with low compression pistons!!! My mini-me has a 10.2:1 comp ratio w/ 125 hp/111 lbs at the wheels and 14.9 1/4 mile.
All this fun for under $500! Great bang for the buck!