V8 exhaust manifold studs/bolts
#1
#3
It would be best to check with the manufacturer of your headers, as you will likely have to use a mix of studs and header bolts. Depending upon how the header tubes run, some are very tight and may not allow the use of studs/nuts. I believe the thread size is 5/16". I found most of the over the counter header bolts from the popular local auto parts stores were too short for my heavy flanged headers and thick gaskets.
#4
A bolt/stud has the same diameter so it shouldn't make a difference. Some of the holes in the head go right into the water jacket so studs will be needed there. All studs may make it harder to install headers due to clearance issues. You have to go to a real parts store that has different length studs. They are usually found in the hardware bins in plastic packages. Most stores today have them behind the counter because people tent to "pocket" small items. Get a measurement of what you are going to need prior to going so you know what to look for.
#5