In case someone is wondering how to drill the two holes in the chassis for the Tc3 rack. Its easy...
Pull two flat head screws out of your front and rear tranny cases (the screws that hold the cases to the chassis for a total of 4 screws), place a Tc3 chassis against your Tc4 chassis (flat bottom to flat bottom) and use 4 button head screws to hold it in place with the 4 tranny case screw holes.
You now have a centered template to drill the two Tc3 rack mounting holes. A countersink bit for the two holes is found at Lowes for less than $5. Take your time with the countersink bit... they tend to wander, and a countersink bit with a center pilot guide has a tendency to open up the hole you just drilled. Just check to be sure the screw is centered in the hole frequently during drilling.
The chassis ribbing you need to remove is minimal, refer to the pics for max rack throw.