Question can never be answered as currently written.
By 870 I assume you mean the Model 870 shotgun? If so, there would be no purpose for that type of conversion. Shotshell primers are of the 209 size. The 209 "conversion" is done with muzzle loaders. The idea is to replace the muzzle loader nipple (that holds the cap) with a conversion unit that uses the 209 shotshell primer to get more positive ignition of the black powder.
Yes and is very worth your while to install it...google Badger Ridge Remington 209 conversion kit. Badger Ridge has the best one, and has lots of blog pages and videos about it.
Try gunshops, gun shows, want ads, for sale ads, on line auction
Cabela's or Dixie Gun Works would be your best bet, or gunborker website.
Armurier Lavaltrie inc 111 St-Antoine Sud Lavaltre Quebec Canada J5T-1C1 450-586-1305 You can get the Remington 700 ML 209 conversion kit and replacement nipples at http://www.muzzleloadingbullets.com/remington_700ML_209_conversion_kit.html It also talks about being able to use the Variflame primer adapter with it. Hope this helps.
Buy a conversion kit and follow the instructions. If you can not do that give it to a qualified gunsmith to do.
Yes there is a conversion kit for the Remington 700 ml. I need one and have been looking for them all over and I have just found them at these two sites. The direct links are as follows: http://cnejsblackpowder.com/store/ml700kit.html and also at http://www.shooterschoice.com/Rem209Special.htm Can find them easyly here : http://armurierlavaltrie.com/ or at this adress: http://armurierlavaltrie.com/remkit.html I found this Remington 700 ML 209 conversion kit and replacement nipples at http://www.muzzleloadingbullets.com/remington_700ML_209_conversion_kit.html It also talks about being able to use the Variflame primer adapter with it. Hope this helps.
Gun shop, gun show
The 209 throws a much stronger spark into the powder charge than a no.11 or musket cap.
If you are asking about a Nitro conversion kit. (Piston) it cost about $110 for the kit. If you purchase it already in the rifle it adds around $50 to the cost
No.
You can buy a conversion kit from your local Plumbing supply store.