I have recently modified my older junior bench extractor to handle 4
shallow frames.
 
If the distance is increased by 3/4" between the top of the stainless steel
basket and the casting connecting it to the driving shaft, which is cutoff
by the same amount, four shallow frames can be extracted at once.
 
A stainless steel plate can be easily built and used as a spacer connecting
the basket to the castings.
 
One shallow can be removed and the other frames can be rotated inside the
basket with these modifications.
 
Best Wishes
 
Dennis