Randy,
Please don't take this personally but I'd like to critique your bracket if you don't mind. I've been lurking on this thread but can't bite my tongue any longer. I totally agree with your general idea of more than one mount point, just want to point out some other things to improve what you've started.
First thing though would be to address the way a G50 should be mounted. It was designed to be mounted in at least 2 places, anyone that is using the 4 bell housing bolts alone is asking for trouble. Just look at the bell housing with it's swiss cheese of holes and it's easy to see it needs more mount points.
In addition it is also a problem if you have some mounts that are rigid and some that are flexible. Make them either all rigid or all flexible. If you mix rigid and flexible all the load under certain instances will go to the rigid mount. Vibration fatigue will also be concentrated on the rigid mount.
Let's start with the thickness of the materials you've chosen. Look at one of the original cars if you ever get a chance. All the brackets on the chassis are made from the same or nearly the same gauge as the chassis itself. Just guessing but it's probably about 18 or 20 gauge sheet. That's max .050" or less that 1/16" thick. Granted most of these brackets are flanged and have doubling washers at the holes. But this gives you a starting point on what thickness is necessary.
The washer doubling at the hole brings the thickness (only at the hole) to about 1/8" so if the entire bracket is 1/8" then it's overkill but acceptable for our purposes because flanging and doubling is very labor intensive. So if you follow the intent of the original car then no steel bracket anywhere on a GT40 replica should be over 1/8" thick. If it becomes necessary to go past that then it's likely to be compensating for less than optimum design.
One other point before going to the design aspect. Please don't trust the home builders for steel supply unless they can guarantee the alloy of the steel . 1018/1020 is a minimum. Look for a local metals supplier or go with the likes of McMaster Carr. There's bed frame angle iron alloys out there that are inadequate for anything approaching a racing application. This goes for graded bolts also. The Chinese suppliers to the home builders are notorious for fudging the actual grades.
Once we've decided that 1/8" is adequate thickness let's look at the other dimensions. I have a general rule of thumb for a bolt hole bracket loaded in double sheer. The distance from the edge of the hole to the outer edge of the bracket should be equal to the diameter of the hole. The shape of the edge should be a radius with the centerpoint common with the bolt hole. The base of the bracket can be wider so as to form a rigid triangular shape. So to refine your existing 1/8" bracket without starting from scratch just round off the 90deg outer corners. They are just adding weight without adding any additional strength. While your at it do the same to the rear of the trans case, the 90deg outer corners where the rear of the trans was cut off could be rounded to shave weight.
typical 1/8" thick bracket
typical original GT40 1/16" thick flanged/doubled bracket, an example of why these cars weighed very close to 2,000 lbs., this bracket takes about twice as long to fab as a flat 1/8" piece.
The main part of your bracket could be treated in a similar manner, round off the sharp outer corners. This area of the trans case where it bolts together is very rigid, you don't need to add any additional strength. The only strength you need is whatever is adequate to transfer the force from the case bolts to the rod end bolts. So think about how much load the one rod end bolt on each side will hold. That's all the load you need to transfer to the case. You could probably could get by with bracketing off just 2 of the case bolts on each side. 3 on each side is somewhat overkill but if you didn't want to start from scratch then at least remove the piece that connects the bottom 2 case bolts. It's adding only weight and no strength.
If you wanted to start from scratch you could go with 1/8" plate bracketing off just 2 case bolts on each side. This would mean you would have to locate your double sheer rod end bolt tabs as close to the case bolts as possible and still have room for the socket/wrench.
Another thing you could do if you didn't want to start from scratch is just swiss cheese your existing bracket. 1/2" holes, spaced no closer than the diameter distance of your rod end bolt hole from any edge, and 1/2" from each other. This is one method to reduce the weight to what a 1/8" thick bracket would be and in some loading situations it would be stronger.
I applied these methods and others like them to get my car to 2200 lbs. (wet) Considering the original cars were around 2000 lbs for the MK1 this is going in the right direction if you really want to call it a race car.
