OK, I see what you want to do.
You will need all the metal work and woodwork off the EL to make everything fit properly. The mag tube wont fit into the slip fit joint of the B-1886 receiver, but you may as well do what I did there. I had the smith turn off the shallow threads on the mag tube so that the mag tube became a slip fit in the receiver. The other thing I did was I used the magazine tube stud from a Marlin 1895 (half mag model) and had this dovetailed to the barrel, then silver soldered in place. I also had the forend tip tenon silver soldered in place. Your smith will need to modify the magazine tube plug to fit over the Marlin magazine tube stud and a screw made to keep it all together. These basic changes radically improve the rifle's ability to retain the magazine tube assembly under heavy recoil. The screws holding the mag tube in place on the B-1886 are a weak point.
As mentioned the buttstock needs a little inletting to fit. I had one fitted from an EL to my B-1886. It is really worth doing - it is so much more comfortable compared to the carbine buttstock.
When I did my conversion I never fitted the forend as I converted a B-71, which has a beavertail forend, and this offers a bit more forend to hang on to. That should work but I don't know for sure.
You then need to have the Winchester markings removed from the barrel and have it re-blued. If you silver solder the two fittings to the barrel as I suggested above you'll need to re-blue the barrel anyway.
Before you do this you might want to check with someone like Turnbull and see if the trigger interchanges. It would save you a lot of messing around. His conversion works out a little expensive as they insist on CCH the receiver as the welding to the tang may show some discoloration.
