On 6/18/2018, Mike Davies in the UK wrote:
Last year I replaced the front drums on my wife's wire wheel MGA. The car then exhibited a serious steering wheel vibration at around 60mph. My local MG expert confirmed the problem and proceeded to balance and re-balance the wheels, swap wheels front to back, check alignment all without success. He noticed some circular marking on the new drums. The wire wheels were bottoming on the drum not the axle cones! I took in the old drums and sure enough there is a groove in the original drum outer face to clear the wire wheel center which is not on the new part. The solution was to have a groove machined in the new drums to match. Now the wheels seat on the cones and there is no steering wheel vibration.

Photo at right shows original front brake drum on MGA 1500 with wire wheels. Notice the cast in groove just outboard of the bolt circle. On the new replacement brake drum, the inboard end of the wire wheel hub hits against the face of the brake drum, preventing proper seating of the inboard alignment cone. This causes wheel misalignment and shimmy while driving.

New part that does not fit, below left.
Proposed solution, below right.

Moss Motors has been notified about this problem, and they will be looking into it. Meanwhile, keep an eye open for this problem if you buy these parts.