Very nice job on this gun...really the only "upgrade" lacking is a metered propane system. A gun this nice really begs a proper propane injection. If you don't want to build a full on-board meter and tank, you could go with a simple external meter/injector system. Here's an example I've come up with...it works great, cheap to implement, makes the gun a lot lighter....
Also, your ignition could be improved with a additional spark gap.
Welcome to Spudfiles! Beautiful gun there.