Exhaust manifold bolt holes stripped

[Redland1]

I replaced gaskets and bolts on the exhaust manifold a couple of months ago and when I was torquing I the bolts three kept turning. I ended up putting in helicoils. Recently I started to hear a loud exhaust leak and isolated the cylinder from where it was coming from and retorqued the bolts but the lower one just turned endlessly which has a helicoil. I’m thinking of drilling it out to the next size up and using timesert’s on all bolt holes so I don’t have to deal with this again. Will be ordering a new manifold,and gaskets. Will drilling it out to the next si.•ze up and putting in timeserts work ?
Also is there a drill guide or something to get a perfectly straight hole ?