Sometimes it's hard to judge. If selling somewhere like gunowners.com, I'd price it at the maximum you'd want to get for it, then be willing to take offers. Set a price in your mind.
You might be able to put the old stock back on, sell it for say $400 or so, then sell the Boyd's stock separately.
They're very good rifles, it just depends on the market in your area. I've sold stuff in 5 minutes I thought I'd priced too high, and couldn't sell something I felt like I was giving away.
Look on Gunbroker and see what they are going for (ones with bids) and that might help you out.