This may help you (I just finished the exact same bike recently)
1. Take the studs out. Go to a hardware store like Lowes and screw the stud in to one of their bolt measurement things and replace the stud with a matching sized metric bolt to go on the universal motor mount. (make sure if you can to get or make a curved plate like in the photos, this bike is a tight fit.) I managed to build this without a slant head.
a. Take the studs out by using a 2 nut method and begin to unscrew the one closest to the engine. (screw them both onto the stud)
2. I had to use a small vice to shape my u-bolt in sort of a V-like shape, like the down tube on the bike is shaped. I placed something in between the U-bolt while it is in the vice as I closed the vice and squeezed it. this was to keep the threads straight as I closed the U-bolt gap (my U-bolt was a 5/16 x2" x 4.5) zinc plated one.
3. Once I shaped the Ubolt I then had to file the 2 holes in the motor mount plate (where the ubolt goes) closer together with a round metal file to allow the newly shaped ubolt to slide through.
3. The extra u bolt length I just cut off with a "cutoff tool"
Now this worked pretty well for me, it takes some elbow grease but worked.
You will probably need to get a "Z" or "offset" intake manifold to get the carburetor to fit on this bike. I do not have a slant head to I had to shorten the spark plug boot and shave the boot head a bit.
it runs great! good luck to you.