Wiselite Arms made the Colefire in two receiver lengths. The long Colefire receiver is the same length as the Mk7 pistols and can be adapted to take the polymer stock by changing the endcap to the spigot type and changing the latch housing to take the locking pin.
I am not sure if the short Colefire can be adapted to take the Sterling polymer stock.
Welding, brazing or bolting a stock adapter to the endcap should work. If you go with a bolt through the center of the endcap, you could also add a Mk5 type buffer with no trouble.
I am not a fan of the PAWS MINI front grip. The angle is just not comfortable for me and the way it swivels freely…. I just find it really awkward. The vertical fixed Sterling “Black & Decker” type grip is a lot more positive and comfortable.