Darren,
The 1/2" studs are more than adequate for your application. We rate the KB Street HEMI with 1/2" studs at 2,500 HP. The early blown fuel engines all had 1/2" head studs.

Aside from that we do not stock 9/16" studs for the lengths required for this set-up. I just received a quote from ARP for a customer of ours that needs a special set of studs for the heads he has. He is thinking of going from 7/16" to 1/2". The cost for just the studs is around $1,700.00. A set of 9/16" studs would be somewhere around the same price, 6-8 week lead time. If you have any other questions please let me know and I will get some answers for you.

Regards,
Ken Black