It's safe to say that the Swedes invented alloy steels of various types, and the fasteners they use stock are of a quality that many car manufacturers only dream of. Even their torque to yeild bolts can be re-used five times. The B20 and B18 bolts, if they are free from rust pits, will last forever.
Studs are used because the coarse thread is used in the block, and the upper end of the stud uses a fine thread, which gives a more accurate torque value and therefore a more even and better clamping load. But on these engines that isn't needed.
Clean the threads in the block with a tap, wire wheel the bolts, lightly oil the threads and under the bolt head, and install the cylinder head.