Have a look at the PST jets website, there was one converted with a PST-600 which you can see the engine install.
Its the tiger paint scheme on the third row.
The main thing for a spectre is to keep the weight down but fitting a turbine like a 600R you should get it around 13-14 pounds and it would fly great!
one thing on the kit I would change if fitting a turbine would be to mount the aileron servos in the wings with a short pushrod and also
add a extra former to the rear of the fuse where the rudder is glued to strengthen the tail section.
I wanted to do the same with a PST-600R but can't get onto a kit now

http://www.pstjets.com/gallery1.html

Cheers Pete