Hi pip I don’t know as the information will be of any use or not but I have an a400 xplor light that came with attachments for a sling already in place so it could be as simple as replacing the end cap but think you’d still need to drill the stock
Have a look on Beretta’s e-store . Easy to order delivery is only a few days , I had a recoil pad sent a couple of weeks ago faster and cheaper than the local gun shop could promise . I got an email saying there’s a 20% of sale the other day .
don’t worry about drilling the stock , just do it in 2 or three increments at a low speed so you can screw a rear swivel in .
For a sling , I’d recommend a Quake Claw , Quick Detachable , the best , most comfortable , non slip way I’ve found to sling a long arm . and not silly money either .