Can anyone say for certain if stocks, barrels, magazine tubes would be interchangeable between Browning and Winchester 1886 receivers made in Miroku?

Metal yes. Buttstocks no. There is a guy over on leverguns forums that just did this. He ended up taking out a lot of material in the tang area to fit the Browning buttstock to the Winchester tang. I assumed they'd be the same 9ther than the safety but he posted pictures that showed otherwise.

Do you feel certain that a barrel from the new Winchester 1886 EL would fit a Browning 1886 SRC? Some have suggested that the threads may be different.

I’ve had a barrel from a Win 1886 EL fitted to a Browning B-71. I’d imagine it would also fit the Browning 1886 SRC. In fact the profile and length of the Win 1886 EL barrel is identical to the Browning 1886 SRC barrel. The front sights are different. However, the EL is a half mag and the B-1886 is a full length mag, so magazine hangers etc fit differently. The barrels have holes in different places and provision for the different magazines. The other issue is the barrel is engraved Winchester vs Browning. I had the writing removed, the barrel engraved Browning and then reblued.

With the B-71 the magazine arrangements were similar to the EL, so the only issue was removing the Winchester engraving.

I have also had a buttstock from a Win 1886 EL fitted to a Browning 1886. It needed some minor inletting to fit the Browning. It wasn’t a drop in fit.

What is it you are trying to do?

Edit - the mag tube on the EL (and the B-71) are threaded to screw into the receiver. The B-1886 mag tube is a slip fit in the receiver.

I am wanting to take the Browning SRC that I already own and turn it into an Extra Lightweight rifle (rapid taper barrel with good sights, straight stock with shotgun butt, half mag) I really like the Winchester Miroku EL but despise the safety. I know the safety can be removed, tang welded up and hammer replaced, but from what I read, the trigger mechanism can not be changed to original Winchester spec like the Miroku Browning. In short, I want the Winchester EL only with the Browning receiver.,

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.