When I fill out forum 1 do they accept it if I put 7 to 11.5 inches for the barrel length?
And what would the overall length be with those barrel lengths with a 6 position adjustable stock?

just put a fixed length down.  Don't put a range of possible lengths, as that may result in your form getting kicked back.

What would the OAL of a AR15 with a 11.5" barrel with a 6 position adjustable stock?
I come up with 31.75 but that does not sound right.

My 4 position SBR AR with 11.5" barrel is 30.5 so you should be about right.

What would the OAL of a AR15 with a 11.5" barrel with a 6 position adjustable stock?

Colt says their 11.5" carbine is 30" with the stock extended.

Yeah, you do not need to register a range of lengths on an SBR.  It's a myth, and an annoying one at that, that you have to register all calibers and barrel lengths you wish to use. People try to cram all this info on to the Form 1 thinking they'l be stuck with whatever they put on the Form 1.  Not true at all. An SBR is an SBR regardless of length or caliber.

The barrel length on the Form is for identification purposes, it does not in any way effect what lengths you can use.  ATF "asks" that you notify them of permanent caliber or barrel length changes, but it is a request, not a requirement.

Essentially  when you get your Form 1 approved, you may install ANY length barrel on the gun and change it as often as you wish.