OEM studs are 3/8"-16 on the end going into the head, and 3/8"-24 on the end that takes a nut (no, I'm not sure why, either.) You can make new ones out of 3/8"-16 "allthread" - I used brass, because I like it more for exhaust work. Cut to 2" or 2-1/4" long.
Screws are, as I recall, 3/8"-16x1-1/2" or 1-3/4". I favour brass or bronze for those as well - there are a multitude of my posts on the subject, and someone started a thread - I weighed in on the engineering reasons for doing so.
MAKE SURE you either put those little dish washers back on, or get new ones! I'm working on a useful substitute using Belleville Spring washers (which are better for the job, but a touch more expensive. Saving a few pennies on job isn't much - saving a few pennies on a half-million repeats does add up...) to more evenly distribute the clamp loads and prevent side load on the screws due to differential expansion of the intake and exhaust manifolds - but I haven't gotten round to it yet. Expect a writeup on the WiP website (link in sig) when I finally do...
5-90