W2 Heads for a 340 Block...

It would depend on what parts you already have as to the cost...you can use our CC article to guide you on cost, just figure the W2's in with the added porting.
The heads on the engine I just did had a fair amount of porting done, just not a full port.

Too much porting will kill that bottom end - midrange power and move the power up too far for a street car.
With more cam and compression you can make more power. I would use a solid FT cam before a hyd. roller if it were mine.
Yes it ran fine on 91 actually!