asking for advice on installing 426 hemi into 1973 340 'Cuda 4 speed

[RUNCHARGER]

That looks fantastic. That's the best way to do it and I'm confident that will mount the engine correctly. One thing I do when I swap any engine into one of these cars is when I mount the engine and rad and shroud in the car for the first time is measure your fan to shroud clearance at 4 points, that will ensure the rad and engine are sitting correctly.
So many times over the years I've read on forums that guys were having problems swapping Hemis in and running into shaker issues or fan to shroud issues and it was always aftermarket mount systems, usually Schumacher.
Here's an old shot from 1981 of my Challenger with a Hemi swap and the original bb brake booster. I took a wedge cut out of the back of the original(!) 1970 valvecover to clear the booster. I wouldn't recommend it as I had to go under the dash to pull the booster everytime I set the valves.
Maybe it's getting time for me to build another Challenger.....