Always wanted one of these, the Drum is on the way, have not shot it yet, I have read the mixed reviews, but this is a toy more or less.
Auto Ordinance .45 1927 A1
I have one with the detachable stock. If (when) you pick up a few more stick mags, modify the magazine catch rather than the new magazines. When the SA version was designed, the height of the receiver was reduced by .1 (1/10th) inch. This had the effect of placing the nose of the mag catch higher on the mag.
There are two ways to make use of the SMG mags; alther each mag, or alter the mag catch. If you alter the mags, they are useless to anyone with a Thompson SMG and the number of SMG mags is finite. They are not making any more. If you alter the mag catch, you will be able to use any SMG mag you pick up. The only downside to altering the mag catch is that you will no longer be able to use the 30 round mag that came with your 1927a1.