The convenient thing about the GI Spec AR-15's is that the multiplicity of other parts WILL fit. About the only thing to look out for is GI vs. Commercial butt stocks. If a fixed A2 style front sight is on there it can be replaced with a low profile gas block. Now open your catalogs and charge ahead!

On the front handguard you have a choice to make: plain GI style, GI with Pitcatiny 1913 rail, M-Lok and Key Mod.

There is a simple special tool to remove handguards if there is a fixed A2 in stock. I suggest buy the tool and save considerable aggravation. The free float option (no fixed A2 sight) takes a more sophisticated tool.

Regardless don't go too cheap and definitely don't make your AR too heavy to tote about.