If you go to K&N's FAQ, they state 1 to 4 hp might be possible. They also state that nobody has any proof that their air filter will kill a MAF sensor and that their air filters will not kill a MAF sensor stating " it is both impossible and ridiculous".
Lots of info there.
K&N Frequently Asked Questions (FAQ)
I've been using K&N air filters since the late 80's and never had an issue with using them.
I agree with JAAY, either leave the stock air box or use a 987 air box.