the gun in the picture is threaded for ICD barrels. you can always tell, as the top tube is flush with the bottom tube. when you have a step back of the top tube, then its cocker threaded.
the guns can run on LP or HP, it doesn't really matter as the reg will give the gun what it needs. the key is to find a vert reg adapter, so you can use aftermarket regs.
to get this in top shape, i would go through the gun, and get the following:
after that, there is still a lot you can do but those above are the real keys. though you don't have change the LPR, as stock is decent, but if you really want get the most performance, then you tend to change everything.