I have a truck engine and 2 bolt, 24V starter that came with the engine. The starter is nothing like yours because it has an offset gear reduction - the motor offset causes the interference with the chassis rail.
I have given consideration to rotating the starter but would probably weld the aluminium flange on the starter before (as Matt has done) welding/brazing studs to the cast iron flywheel housing.
I would be interested to know what starter you have, as it could save me cutting my new (to me) chassis. Hmm, maybe the landie isuzu has a different tooth pitch on the ring gear and pinion may be incompatible
Edit: BTW, I meant to add compliments for your work on the adaptors

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