You don't need mod parts.
You'll need to build a spring compressor. It will take about $20 to build one out of a cull 2x6, c clamp, and a couple u bolts and wood screws. Something like this:
http://www.kermitairgunclub.com/airguntips/compressor/ You can use it for pretty much any airgun so it's a good investment. Some guys do the "push the end against your bench while you drive the pin out" and while it is possible, it has the potential to go badly. Unless you like getting stuck with bits of metal and/or looking all over hell's half acre for said metal bits.....
After you disassemble your airgun, you'll notice that there is a bleeder hole in the front of the piston. This is what allows air through the seal. You have a coupel options, from jb weld or epoxt to tapping the hole and loctiting a screw into it. Either way, if you plug that hole, you'll get about 650fps. After that, you canput a little pre-load on the spring (a washer or 2 on the spring guide or a new spring guide) to push it to about 700. After that, you'll start wearing out springs rather quickly.
Don't believe the 900 fps claims for most .22 spring guns, it's really not possible unless you use zinc/aluminum/plastic ammo. Using that stuff can seriously bugger up a powerful spring gun (think of it like dry-firing a bow).
About the lockup of the barrel, there's not a whole lot you can do easily other than just use the sights. Since they're mounted on the barrel is doesn't matter if it locks up exactly the same every time. When you mount a scope on the tube, then you might start having problems. The Benjamin at CT (if it's the one I'm thinking) is just a Crosman Phantom in a different stock, which is a $100 gun. It shoots like a $100 gun

That said, I have one modded in this way, and it will take out a crow within 35-40 yards. pretty much all I need it to do.