Is this an older three hole action or the newer "4 whole" spacing? If its the older three hole action I think your options in a one piece rail are limited to something like a burris/leupold turn in style base. If its a 4 whole action then there are several makers of one piece picatinny rails, of which I like Warne for a well made product at a good price.. I ran a one piece base on a model 7 for awhile but replaced it with Talley Lightweights because the rail made it difficult for me to top load the internal box magazine because of the smallish ejection port, this may or may not be an issue to you. The other issue could be comb height. Using a one piece base may make it difficult for an 11 yr old to get a good cheek weld with a factory type stock, which are rather trim without a lot of comb height. Again, that may or may not be an issue for you or one could build up the comb with a stock pack or foam/duct tape method.