I have a pre-assembled YHM upper.  It has the YHM Diamond Series (Specter Length) handguard..  I am interested in switching to the Troy Alpha 11".  Now, I understand that the YHM uses a different barrel nut, so I'd have to switch barrel nuts (so I'd need two different barrel wrenches).  Can someone tell me what else I need to know about making this switch?  I have never built an upper myself, so I don't know much about gas blocks, gas tubes, etc.  I believe my upper has the specter gas block.  I don't think this will work with the Troy, right?  If not, can someone please tell me what I need to get.  Thanks in advance.

EDIT:  This is the upper I have.

Check Here

Okay, thanks.  How about switching to any handguard that doesn't use the YHM barrel nut?

Pretty much only YHM forends fit YHM barrel nuts, unless you find a rebranded YHM forend.  I must ask you, have you actually handled a TROY Alpha?  Those things will eat your hands alive unless you put on those stupid squid grips.  Honest to God, the Alpha is the most gawd awful handguard I have ever used.  It will eat you alive if you slide your hand along the handguard.  It did not earn its nickname 'Cheese Grater' for nothing.
But if that is what you want…
IMO you should be looking at the TROY VTAC or the equally nice, lighter, and thinner MI Gen 2 SS or the MI SSK KeyMod.  Anything but the TROY Alpha.  
The Troy Alpha and VTAC use standard barrel nuts.  The MI come with their own proprietary barrel nut and barrel nut wrench.
If you switch away from the YHM guard you are going to have to use the barrel nut their forend is designed for.  DD M4 has their own, the DD Lite has its own… most have specialized barrel nuts that only fit their forends and some make you buy a special wrench separately in addition to the forend.  Most forends though that require a special barrel nut will supply them though but they often do not supply the proprietary wrench, just like YHM does not supply a wrench for theirs.

The Spectre gas block will not work with either the TROY Alpha, VTAC, or MI Gen2SS or the SSK Keymod.  For all of them you need a low profile gas block. TROYs are the lowest profile, with PRI, VLTOR, YHM and DD set screw models being all tied for second lowest profile.

I appreciate your opinions on Troy and your overall help.  I wasn't 100% set on the Troy, it was just the direction I was leaning.

I just put a Seekins Precision BAR on mine. I was very picky about the mounting system as I wanted it to be rock solid without the use of jam nuts, like some rails use. I also had a specific look/design in mind. The Seekins comes with a proprietary barrel nut but it uses a standard AR wrench. The rail looks great, is rock solid and has 5 QD sling attachment points cut into it. I couldn't ask for anything more - it's perfect for me.

I also have a Troy low profile gas block under it with a black (WMD) gas tube.