As to the skid plate, I have seen a number of guys simply cut off the drivers front support from the skid plate. The crossmember that is rubbing provides a decent amount of tranny pan protection without that corner supported, better than no skid anyway.

As to the spinning nutsert, if it is spinning and you cant get it out, take a chisel or big flat head screwdriver and drive it between the frame and the skid as close to the spinning bolt as possible. The extra downforce from the chisel is sometimes enough to get the nutsert to bite and get the bolt out.

There are a few options for dealing with the nutserts, assuming this is one that needs to be fixed. First is to cut a hole in the frame and tack it into place or weld a new nut inside and then weld the hole you cut into the frame back up. Second is to drill out the nutsert and all the way through the top of the frame, running a longer bolt all the way through. Third and cleanest option is to grind the face off the nutsert, push the top part into the frame rail, use a magnet to get said top part out, and install a new nutsert. Last time I did the nutsert fix we did all of them as the 1/2" nutserts were half the price of the 12mm and SAE bolts are much easier to find. I think my buddy said he got them from the savvy guy (black magic brakes).