vortec heads are very good BUT, they will require a new intake as well, that is another $200+.
i think most vortecs are either 62 or 64cc castings as well, that would drop a little bit of the compression.
i usually deal with a place in bristol, pa called contemporary corvette. they are good people with fair prices on good parts. check them out at
www.contemporarycorvette.com give them a call and see what they in stock.
the corvette show out in carlisle, pa is also coming up next month. you can always score a good deal on aluminum L98's there.
later
tim