Being hit with the 10 post limit again, despite not having anything new posted... 😕

The JG is a TM clone (same as the Cyma) so as far as internals go, standard hop rubber should fit fine but be aware that ones with a longer feed lip (like the Maple Leaf ones) may protrude into the feed tube a bit.   As for barrels, just make sure it has both sets of grooves in the side of the barrel, the hop unit clip goes in a different place than on an M4. ZCI ones will work, or if you want to spunk a bunch more cash, Prometheus do an M14 specific one. You're looking for something around 420mm length. Worth mentioning though that if the cylinder is the same sort of size as a TM or Cyma, changing to a tighter bore will push your FPS up a not inconsiderable amount!

Not that I think this will last long without the Rule 5 picture but it's rather optmistic pricing. 8 mags would be around £400 at retail, without the mod being done.   The seller hasn't specified the generation of Glock 17.   Does the seller think he's being generous by offering to include the original furniture when he's charging above retail for what I assume is the M4 CQBR as the base?