Like many who have come before me, I found the need to mount glass to the heatbed of my "new to me" Makerbot. As each part gives, the MB will slowly become more open source.
That said, here is my solution for the heatbed when mounting a 300x200x3mm piece of borosilicate glass. The one I purchased was from Amazon titled (in case link goes stale):
"Borosilicate Glass Print Surface 300x200mm for RepRap 3D Printer Prusa i3 Upgrade"
These use the existing 4 screw holes that hold the mounting hardware to the bottom of the heatbed along with 4 x 8mm screws. In the design pics, you can see I thought about putting two thumb screws in the front for easy removal. I found sliding it through the right side panel just as easy (and didn't have the thumb screws).
Also, be sure to adjust your Z endstop. You can open the back and loosen the two hex screws that hold it in place. Just slide it all the way down to allow room for glass. You may also print a spacer, such as:
Remember to tighten the bed nuts all the way before manually testing clearance. If not, you may run your hot end into the glass and break it.
12-21-2018 UPDATE: Added a "bracket" version that connects the front and back clips together. I have not printed yet, but should align and allow the clips to not rotate under strain. Also, recommend higher infill due to heat, so 75-100% should do (only time would tell).
12-27-2018 UPDATE: Had time to print the bracket and made some modifications. Allowed the bottom to come off the plate to hopefully reduce warping. Also, made some adjustments to alignment. Should mount to existing screw holes easier. I printed at 75% PETG without any issues so far.
Print on side, no need for supports. You will also want to print these with ABS due to most other materials' transition temp being to low. I printed mine initially in PETG on my FT-5 as the MB would not print well enough on the warped bed.
Designed in Autodesk Fusion 360