Originally Posted by ShadowTwoSix
No probs! Something to consider is that like US groups, it wouldn't be inconceivable for CANSOFCOM members to have one lower and both a CQB upper and a 16.8" upper and switch them out as needed. I can't confirm that, perhaps someone else here can. It would certainly make your build easier. You could even build a 2nd upper and have one for CQB & one for field play.
What I'm doing now is that I bought a M4 with CQB length (10.5in or CQB-length barrel) and start the modification from there on. In other words I'll use a regular receiver + RIS + CQB length barrel. I hope this is still acceptable as CANSOFCOM C8s
I looked into IUR just now and realized it's too much of an investment now if I replace the totally new an unused RIS+ upper for a IUR, which is another additional $100-200 investment.