Starter to block interference.

If you mean it's hitting that cast-in boss on the block behind the starter, then yes, it's a semi- common fitment issue when swapping to a mini starter. That drilled boss on the block is just there to locate the block on the factory machining jigs when it was originally built, and is not necessary in any way, shape or form anymore. Simply grind it down until you have enough clearance for the starter to mount squarely.