I have a Colt LE6920, I am looking to put a folding front sight on it. Any suggestions on a good replacement? I would like to stay with a gas block type. And how hard are they to replace?

thank guys...

Congrats on your first post!  
 
I have a 6920 too, and I think the YHM  (Yankee Hill Machine) Front Flip Sight Tower would look very nice.   I like the hooded version for $97.00.

Just my personal opinion though.  

There are lots of options out there...

Bayonet lug or not, extra rail space or not, bolt on or pin on...etc.

They are not too hard to remove and replace if you do a little research and have the right tools available.

Sounds to me like you bought the wrong rifle.  Probably should have bought this one instead:

Colt 6940

In all seriousness though, I would be really careful not to mess up the reliability and durability of my rifle by going away from the factory pinned FSB.  I know you said you wanted to stick with the gas block type, but if you absolutely have to have a flip up front, I would shave the factory FSB, slip on a longer FF rail to cover it, and use a Troy flip-up front sight attached to the rail.

Here are a couple of on site guides to give you an idea of the work involved -

Assemble your own LOWER, UPPER, FREE FLOAT, TRIGGER, GAS BLOCK - Step by step instructions!    

Scroll down the page to the instructions for "Install your own free-float rail system, step by step" - This will show you how to remove a front sight base (ignore the stuff about barrel removal )

Using the same link above you can also scroll down to "Make your own cut-down low profile gas block, step by step"


Hope it helps!

I use the GG&G bolt on flip up gas block on 2 of my guns and they are super durable hunks of steel...quick too.

I think that I may go with the AR-15/M16 #41-B SILHOUETTE FOLDING FRONT SIGHT by A.R.M.S.,inc it keeps the factory look that I love about my 6920.

http://www.brownells.com/.aspx/pid=26728/Product/AR_15_M16__41_B_SILHOUETTE_FOLDING_FRONT_SIGHT

thank you again for all the help!!!