Case savers as Araon said is the best way,helicoils are more awkward to fit and aren't usually that long.
You can do it yourself,best to remove the engine,although it is possible to remove heads and barrels in place,it's not worth the effort and you'll bend the tinware anyway.
Get the engine out,strip it down remove the barrels.Any stud that is longer than the rest you should do.I would do all the lower 4 studs on each side anyway whilst you're there.
You'll need to buy a set of case savers I got some from VW Heritage which came as a pack of 8 (enough for all the lower studs) Check if your's are 8 or 10mm.
Remove all the studs for that side anyway and check them,also makes it easier to tap the holes with no studs there.
Then cover all the case holes for the pushrod tubes and barrel holes etc.
Drill the hole until you just reach the end of the hole allready there.I used a vacuum cleaner to catch the swarf as I drilled.Make sure you drill straight.
Retap the hole with a plug end tap,not a taper one as the taper one won't tap to the end of the thread.Use plenty of grease to catch the swarf.Clean the hole and blow with compressed air.
Then fit the case saver.What I done there is lock two head nuts together on a head stud with about 15 mm of thread showing,screw the case saver on to the end,then lock two head nuts on the other end and screw it in.Don't force it when it gets to the end though or you could damage something.If you end up with a bit sticking out you can carefully grind the end off with an angle grinder.
