summit has brand new assembled GT40-P's for $539.00.
as stated by 4-banger boy
, you will need a different set of headers that run about $200.
But if you want to port your stock heads, I'd highly suggest NOT using a dremel. You'll be porting for about a week straight that way.
When I did mine, I used a high speed die grinder with a carbide bit and I still put in about 11-12 hours of porting. Its worth it though, i like the look on peoples faces after I whoop their car and tell them its got stock heads
good luck,
-Drew