I've got a very crude DWG 3D model of a 302 that includes the engine mount bosses (and some other stuff). Some of the surfaces are missing, but that shouldn't effect what you need. E-mail me at [email protected]
The temperature variation from side to side is way too much. Measuring the temperature of each pipe near the head will isolate any cylinder that's weak. Something's not right, either mixture-wise or even no ignition at all.
The biggest weakness (torsionally) that I see is through the area near the front of the side "pods". The structure needs something to tie the two pods together like a large transverse box well connected to the side structures.
Note that all those engines really have the same cylinders firing 90 degrees apart, just in a different sequence. If the tube lengths from the heads to the collector are equal, the same layout into the collector will work, no matter which engine.
You are assuming a single 5/8" master cylinder to operate both front and rear brakes. Typically, there are two masters on a balance bar system. The balance bar geometry decreases the force into each master cylinder by roughly 50%.