I have a Lee Speed sporter that had been rebored to 35cal on the 303 case. BUt who ever did the work never completed the chamber work.
So I pulled the 35-303 bbl off and set it aside till (?) and in the mean time installed one of the Ishapor 410 SMLE bbls in place. The bbls were cheap,,$15 IIRC some years back not long after the flood of the IShapor 410 SMLE's came to the USA surplus market.

Threads are the same and clocks into position just right. I had to open the IShapor extractor cut in the bbl from it's rounded profile to the LongLee squared cut. The SMLE bbl profile is the same as the orig LeeSpeed bbl that was on the rifle.
I lowered the SMLE front sight some as I was shooting under clay targets at skeet.
It actually feeds a second round out of the magazine, though occasional balks are to be expected.
Not quite 'Mad Minute' ready.
I use and reload 410 2 1/2" shells though I think the Ishapor bbls are rechambered to US 410 3" chamber.

Fun gun,,draws some stares on the clay course.

Have one of the Ishapor 410 single shot SMLE's also but it does;t quite leap to your shoulder as the Lee Speed does!