Hi Frenchy;
With mine, I used 2 nuts tightened against each other on the stud and they came out with very little effort even tho they were original installed studs.
Also, I expect u will get several replies like this one, but if you do install the alloy sump cover with a separate screen u will have to be careful to get the hole in the screen aligned with the scavenge pipe as u did with the original cover. If it doesn't line up on the first try u can try flipping the screen over. This happened to me with the SRM cover. If not aligned correctly the ring on the screen could partially block the pipe and allow any bits of gasket sealer, etc to restrict oil flow to the oil pump. Anyway, whichever cover u get will require longer studs or bolts as the new cover is thicker. SRM supplies them with their kit.
HTH Gary