Head Studs..Question

[jg61hawk]

I posted previously about removing the head on a old guys car...
https://www.fordbarn.com/forum/showthread.php?t=312505

4 studs came out with the nuts. We ordered all new studs. My plan is to replace ONLY the ones that came out. I can also use the old ones. The questions are:

Do the studs have a torque value...or just double nut and tighten?

Is there a problem mixing old and new studs?

Any other comments are welcome.