New starter

I've done both.
As for modifying for a mini, it was super simple. Mostly just some cutting with a sharp knife.
But, it's really not necessary to go to the mini with a /6. The up side is that they are readily available and not terribly expensive.
The original starter is great choice also. There is nothing quite like that sound a gear reduction starter makes. You stand a better chance getting a car started with a low battery with one of those.
The really nice thing about swapping off a /6 starter is all you got to do is put the hood up. No jack required!
My personal preference; go back with a gear reduction starter.
The mini is the way to go if you have a V8, and sure makes the job easier, but a /6 just doesn't need the mini and they're also very easy to get.