All the Volvos I have had came with head bolts, not studs and nuts.
I have never replaced a headbolt unless there was a reason for it to
be faulty and I have only broken one in about 40 years of working on them.
That one failed upon torquing because there was rust in the hole and it
was distinctly a torsion failure. Since then I have run a tap into each hole
to make sure it was good and clean, then put a little grease on the headbolt
threads and under the shoulder of the head when I installed them. BTW I
cleaned the threads and the shoulder (or the whole bolt) using a wire wheel
before installation also. Torqued in accordance with the manual as far as
sequence and torques, 29, 58 and 65 foot-lb. Worked great for me. Sometimes
I have later retorqued them all to 70 ft-lb but never more.

BTW the OEM headbolts that come with Volvo engines are excellent quality bolts.
--
George Downs Bartlesville, Heart of the USA!