Shouldn't be a problem with an impact driver, those screws all over the engines tend to strip not using one. Shouldn't be any loctite that early used but if a PO has been in motor? Even so, the impact driver should move loctited parts too unless the superstrong stud and bearing type used. The loctite will melt if screw heated but touchy as too long with torch and other things get damaged. Any seals or o-rings there local will go first.
Make sure the impact driver is switched the correct way, common to have them TIGHTENING rather than loosening. Mine is actually marked backwards from the maker, it tries to go tight with it on loosen.
One can often take a sharp flat blade chisel & hammer and dig into screw head on the outside edge to angle sideways in direction to get it loose. You'd best be good though, if not done exactly right then you actually stake the screw in place harder rather than loosening it. The chisel must be super sharp to dig in very easy with as little peening done as possible, if you peen the OD of screw down, it locks harder in place. I start not at the very edge of screw but in a bit, do the very edge and it locks in place worse. You want enough thickness on screw there to hold any deformation to the screw rather than transferring it to the material underneath. Don't punch straight in, try to start sideways in direction to loosen.
Screws are not that hard and a pilot dent is pre-made made by stripping them out, drilling may be necessary-of course the mess.
That type of screw tends to really lock down well with zero loctite and why they are used there. Don't want them coming loose. Look close, they may even be peened in place like staking, a small round sharp punch sometimes used to punch a small mark to lock them even harder.