The twinlinked drone pulsrifles are not hard to copy as they can be found on the Tau Piranhas from the Recon Pack still available from FW, problem is more with the top hatch as you need an existing turret to copy from.

To answer your question:

Instant Mold is very easy to work with, put how ever much you need to use in very hot (I use just boiled water from a electric water boiler) water for 1-2 minutes, take the Instant Mold up (its a bit hot, but you will not get burned from the Instant Mold, ofcause the water is hot, so I use tweezers) press it against the subject you want to copy, and let it cool down (takes a few minutes), if you fold it it will stick to it self and you will need to cut the Instant Mold open.

Mix Green Stuff and Miliput (I use the standard one) 50/50 and press it down into the form you just made, let it harden for some hours, I usually just let it sit through the night, and you are done.

Just trim the copy you created and glue it on to whatever you want.

Mind that in Denmark this is not illegal, you are alowed to make copies for own use, but legislation might be diffrent where you live, so look out for that.