So, I might have a small problem but maybe not, I am building a CMMG 4.5" .22 upper. I bought an ALG 10" upper ( meant to order 8"), the bbl will be 4.5", DeadAir Mask is 5.1" and I plan to get the Gemtech QDA 4lug adapter at 1.15", this adds up to 10.75" just a mere 3/4" longer than the rail.
Do you guys think 3/4" will be enough to use the 4 lug adapter easily enough? Or should I just go ahead and order an 8" ALG rail or look for other 8"-9" rails?

Just wait. If it doesn't work, then order the 8" rail. You know you're going to build something else with the 10". It's just the way it is. Spare AR part = another AR.

Actually this adds up to 9.75"... barrels are measured from the end of the barrel extension to the tip of the barrel.

CandyMan is correct, I received the ALG EMR V2 and for the price you can't beat this rail but I am going to need a shorter rail.

Placed another order into ALG for an 8" rail.