Why hope when knowing is much more comforting. I would not take the chance on wasting my money on the Clark handguard. The potential aggravation and downtime of having to deal with returning it would not be worth the slight savings(weight&cost) IMO.
Since cost appears to be a factor, buying used might be a good way for you to pick up parts for this project without breaking the bank. If you watch the EE can pick up a Daniel Defense handguard for a little more. Sure, it will weigh a bit more but the structural integrity will be there beyond a shadow of a doubt.
Rob made a very good suggestion by recommending that you go with a LW barrel for your build. There are plenty of people that are using them with no ill effect.
As IG said it’s your money so do as you wish but in all three of your threads that are centered around your backpack theme people have offered you very solid advice. It just might be wise to give some of it a bit more consideration.
As far as your pack goes take a look at US Grunt Gear. They make some darn good stuff. Cost could be up there but I think you would have a good chance of getting what you want.
http://www.usgruntgear.com/custombags.html