Ok. An honest (in my opinion) value on the rifle.
Base rifle (used) $200
aftermarket stock (used) $75 (Midway used to carry the fancy, fully adjustable Fajen for $109)
Green Mountain bbl $100 (they're $144 new)
I'm not familiar with the value of the other doodads and whatnots you mentioned so let's just say $150
That adds up to about $525 I think.
Offer him your revolver with the extras and $100 cash and see what he says.