These will work with a Mod 1, however, as they were designed primarily for use with the Mod 2 gas system parts in mind, it may be necessary to cut access holes in the handguard after assembly to permit pinning of the Mod 1 gas block.
It comes with a tool that grabs the top pic. rail. You will need a breaker bar to tighten the rail, I used thread locker on mine.
The lengths are exact measurements from Knight's.
Most of the lengths are exact, however the 8.5" version is actually 8.75".
You may be able to but it is unlikely to fit, the airsoft gun would have to be able to use the barrel nut for this handguard.