AccuTriggers are not retrofittable to older Savage actioins. It is possible to have an old reciever milled to accept the AccuTrigger, but then you would have to be able to purchase an Accutrigger from Savage, which is not possible right now. Maybe in the future Savage will offer an upgrade option or start selling the trigger.
Aside from the AccuTrigger, the old Savages have many aftermarket triggers available. I've not used an AccuTrigger, but I'd be my bottom dollar that the aftermarket triggers are just as good if not better. I've not heard anyone say whether overtravel and engagement are adjustable on the AccuTrigger, but I know they are on the aftermarket triggers. So, that puts them ahead in my book.