I don't have a level surface, any time I remove the loader it's a bit of a fight to get it back on.
Bring the tractor up the the loader, get everything aligned and drive in until the loader is firmly in the pockets, curl your bucket down to get bottom settled in, move the boom cylinders in and out, bucket up and down until one side is mostly aligned.
The pins have tapered ends for a reason, get it started in the hole and drive it in with a hammer until it's all the way in. You don't need a sledge hammer, but a decent hand held hammer will be enough.
Once that's done, go to the other side, jiggle the bucket and boom around until it's close, drive the pin in.
So long as everything is close and you use your head, you're not going to damage anything, those pins are under a lot more stress under normal loader use then you'll ever do with a hammer.
Jason