Like all have said, you need to think, then start with a configuration and stay with components that work for that configuration. Carbine buffer tube w/carbine stocks, but either commercial or mil-spec will need to be considered, even though they're both carbine components.
As to grips, you'll probably be changing out a few to find what you want or like as a style/comfort/usage(A2, Ergo, more vertical, A1, Hogue over-molded, and many others). Then there's all the colors for what is called furniture(grip, stock, handguard).
One thing I've seen done that is a little different is going with barrels in either Carbine, Pistol length, or Mid-length w/corresponding gas tubes and putting on a "Rifle" buffer tube/buffer and spring w/corresponding A1 rifle stock.
So, there are some odd changes you can use, you just need to remember what parts are needed to make that combination work properly.
US Air Force 73-77
57th Munitions Maintenance Squadron F4 Phantom
Nellis AFB, Nevada
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