Brewing Pumpkinator at home

I was searching for a Pumpkinator clone recipe to brew with my brother when he is in town for Thanksgiving and came across this thread from 2015. @awinkro was kind enough to share the malt bill, but according to St. Arnold's website that beer uses pumpkin and spices. From what I've read, pumpkin is typically mashed with the grain. I still have a few questions though. How much pumpking should be used, how do you prep it (bake, puree etc...) and how much pumpkin spice should be used?