The arch didn't quite work out for me, so as of right now, the project is on hold. It protruded from the back wall too much to look even remotely natural, so I pulled the plug until I can figure something out. I might cut the back half off of it so that it sits flush with the back of the tank and then use some sure grips to hold it in place, or I may just scrap the project entirely. I think I can cut it in half with an angle grinder, but the arch might fall apart if I try that.
I've got another Vortech cover for the right MP40 coming from Gooch this week, so that should allow me to pull the last of the frag racks out of the tank. I was really happy with the last one Scott sent me, so I may just look into having him build me a magnetic arch for the back of the tank. Some things are just better left to the pros...