windsor jr heads

They are very good heads very durable heavy but durable. They have a very good exhaust port and work well with blowers and nitrous engines. That is a steal for 300 beans. I use these on my Pure Street car N/A and love em. I used them in the past with an X cam an X cellerator and 100 shot and have run bottom 11's spinning. They will work with your current combo and will leave you some room for improvements.
 
if they are the newer windsor jrs (roush 180's) they are definitely worth the 300 bucks and would be an improvement, but I heard the older windsor jrs are not as good. If they are the older version, I don't think it would be worth the hassle of swapping heads of the GT-40's
 
If they are the roush heads, they should be 1.94/1.60 valves. If they are ported and polished, they should easily be worth 25 horse over GT-40's. And the price is very cheap if they really are the roush heads.