I've been playing around with my parts and this is what I figured out;
BARREL.jpg
On the ICS barrel are two tabs which have to be cut off in order for the
new delta ring (barrel nut) to fit. I tried this with a G&P delta ring assembly.
CAP.jpg
The ICS handguard cap is attached to the front triangle sight with a screw
(top hole of cap where normally the gas tube goes through), and at the bottom
is a smaller hole where a pin from the sight sits in. Either cut this pin off or you
can drill a hole in the new cap. And for the screw at the top, the hole in the new
cap is bigger than the screw and really can't be used, maybe put a washer?
The handguards will hold the cap in place just the same.