That's what I was going to suggest...lots of duct tape!
Is this a Atlas bipod?clearly some parts are missing. you can use this adapter as reference.
I found something called a Arca rail that looks like what is imbedded in the stockI have never seen one like that. Following just to see how that attaches.
Where or what do I look for to attach things to it??T-Slot rail. There are two stds for those, Anschutz and Freeland. Given the apparent narrowness of this one I think it is a Freeland. Very common in the High Power and Small Bore worlds.
Freeland Winchester Blank Rail Section 15″ for Target Rifle Stock Accessories - Freeland's Sports LLC
The Freeland's aluminum rail section is designed for Freeland/Winchester type accessories used on many American made target rifles. The rail is blank so you can put screw holes anywhere you want or cut it down to what ever size you need or leave it 15" long.freelandssports.com