Michael,
I made a quick model of the bracket that I used to attach the gas strut to the engine lid. I also made a model of the hinge bracket. Nothing to scale as I didn't drive the Speedster to work today but I hope it helps you get an idea of how I installed the strut.
Looking at the model, the engine lid will be "sandwiched" between the strut bracket and hinge bracket. The 1/4" 90 degree bend ensures that the bracket will not bend upwards and being that I made mine from 1/8" 304SS, I doubt it would bend anyways.
With the bracket installed to the engine lid, you'll install the 13" strut to the hole in the bracket. With the strut installed to the strut bracket, you will now need to open your engine lid to the position that you want it to be (fully open) and then mark the position where the strut will need to be attached to the hinge mount on the firewall. It would be a good idea to protect the paint on the body with something so that when you are opening your engine lid to the full open position, you don't open it too far and scratch your paint. If you currently have the pin that keeps the lid open, you could lock it open with that and set the strut position to where it needs to be on the hinge mount on the firewall.
I attached the strut mounting stud directly to the hinge mounting bracket on the firewall. There is no need for an additional bracket here - only a hole large enought to fit the stud through. (5/16")
If I had the room to install a strut on the drivers side as well, I would probably do so and use 2 of the 30 pound struts instead of 1 of the 45 pound struts but I have no room on the driver's side to do so. The 45 seems to work well but I do sort of like the idea of having 2.
I picked up a number of struts from eBay and paid roughly $20 each with shipping. You can find them all over the place and can surely find them cheaper than $20 if you try.
If you need the exact dimensions of the bracket that I made, let me know and I will put a tape to it when I get home.
Hope that helps you.
Jimmy