As far as a synthetic stock, yes, the set from Midway for the Browning A5 works, but you have to rework the trigger guard tang as the browning has more curve to it. Best to get a different trigger guard from like gun broker on the cheap, heat it with a torch and reform to fit the synthetic. Remember, this is a long recoil Browning design so cutting the stock down is not an option to make it a SHTF weapon. The A5 kits will work, just rework the trigger guard.
The extension tubes for the Model 1100, 11-87 and Browning A5 all work just fine. Two screws (one on either side of the tube) and then it threads out. You can prob buy an old Model 11 (non Sportsman) parts gun for $50 or so on Gunbroker so you have the tube, forearm and stock to replace what you have now.
One word of caution on the stock removal, the action spring tube that is inside of the stock is very very fragile. Once you have the tang and mount screws off... PULL S T R A I G H T back, do not wiggle the stock from side to side. Of the vast many of Model 11's I have seen, a good 80% have had this tube cracked off due to not understanding how the stock goes on. Many have been rewelded. Action spring tubes are rarer than hens teeth and when you do find one in good shape, people want damn near what a beater gun is worth.
The friction ring and spring sets can be bought new from Midway but they are for Browning A5's and work just fine in the 11's. Not much else is interchangable between Remmys and A5's due to metrics Vs inch system. Savage 720 and 740 (same exact gun as the Remmy 11) will interchange. Savage parts are better built than the Remmy, so when ya can, grab up Savage spare parts.
Also know the date of your Remmy as some significant changes were made around 1927 in the trigger, safety and bolt groups and those parts will not fit earlier models.
