Ray, I mainly race on concrete/asphalt. I dont know anything about carpet! I am sure you will get it worked out though.
One thing I forgot to mention on the Parma Alfa was I like to have my bodies sitting as close to the track as possible so try to leave about 4-5mm below the molded in cut line till you get it mounted totally then trim as needed as it does have a more sloped nose and will sit on the shock tower and if you cut it on the cut line it might be a little higher than you planned. I know you can trim the shock tower as well but I like the lower front body cut option better. I am sure that on all other makes of cars the body will fit perfectly with the molded cut line but I think the Pro4 has a taller shock tower than any of the others so you might test fit the body first.