Reasons for using head studs instead of bolts:
1) Unless you have new head bolts, it is normally the case of comparing 40 year old bolts of unknown history with new studs of excellent quality.
2) Accurate torque readings with bolts depend on equal quality, cleanliness, and lubrication of the 10 sets of threads in the block. With studs equal torque is
obtained at the nut end where conditions are easy to control in order to assure the accuracy of the torque reading.

( and BTW, I always have stud sets in stock )

Suggestions on the head:
1) Determine the actual compression ratio by checking the volume of the combustion chamber and the deck height of the pistons at TDC.
2) Have the head flow tested to determine whether the port work actually helped.
3) check the valve stem to guide clearance to be sure this was done correctly with non-stock valves and guides.

I'm happy to answer questions or help you with any of the above.

John
V-performance.com