400 into 73 v8 duster using stock mounts

Nope.
Even the Schumacher swap mounts require some cutting and reworking of the K member mounts in order to work.
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If that's too expensive for you, wait until you get a load of what you'll need to pay for headers... and oil pan... etc.
If you insist on making your own mounts, bolt it all together and lower it into the car, using the transmission mount to locate the engine/trans fore and aft. This will give you a fair idea of what you'll need to cut/move/weld/relocate/modify to make the motor mounts meet the K frame mounts and end up with the engine in the correct position.
The final location dimensions (borrowed from tti's website) are:
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If it's not in the correct location, nothing else is going to fit right.
Even if it's perfect, chances are your BFH is going to get a good workout on other aspects.