J27, Slot= 9 3/8", TD=14.5mm

9  3/8 inch long nylon insert.

My best MastGate for your feed slot is this 3D printed snap-in insert.
I made a video of how to install this type of MastGate but it does not show that you also need to drill a 3/16" hole into the back web of the channel before cutting the groove into the feed slot.

https://youtu.be/VvgMuhgE8TI

Nipple DRILLING INSTALLATION:
The insert sleeve is symmetrical, with two protruding nipple pins. 
Insert a #55 drill bit (or a finishing nail of the same diameter) into each nipple's drill guide hole before centering the insert into the feed slot.
Lightly hammer the drill bit to make a mark into the aluminum back web. 
Remove the insert to center punch the drilling locations.  First, use 1/8" drill bits, then finish drilling holes with a 3/16" drill bit.  Hand twist a larger drill bit in the holes to remove burrs.
Nipple pins of the nylon insert will key into the holes to prevent unintentional sliding of the insert.

REMOVAL:
Top & Bottom ends of the insert sleeve have outer edge notches.  Squeezing notches together with tweezer to pull the insert up & out.   

Save your email ref# pg704a for help
J27 pg704 D1 td14.7 v.107  8/31/21