With that many modifications, I'm wondering why you're using any part of the factory frame? It was designed to flex. I've put many thousands of laps on boxed frames on dirt tracks, and we were constantly patching cracks at stress points until we learned the right way to "box" frame rails. It's not as simple a process as it looks to a first timer with a MIG welder and a bunch of flat stock. You'll also need to install some chain anchors into your shop floor, and compress the suspension to the desired ride height with ratcheting chain binders before tinkering with engine mount angles.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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