Fritz...
1. BEFORE taking anything apart, remove the plugs and roll the engine over taking base-line measurements of each cup-to-cam lobe. Mark these down. Measure carefully, as mistakes will force you to start over.
2. Set engine to TDC #1 during compression stroke. #1 cam lobes will be pointing outward, and you can observe matching marks in the front cam bearing cap and cam that should be lined up. Confirm you are on the TDC mark on the front pulley. I think it says "PMS", but it's been a while since I played with a 115. I generally prefer to un-latch the chain and pull both cams simultaneously, but this requires that you roll the engine around until the master link is where you can get to it, and take extraordinary precautions to avoid dropping any parts of it into the sump via the front gallery in the timing cover/head. Rolling the cam out as described is possible as well. Whatever floats your boat.
3. I use a 1/2" breaker bar to press back the tensioner. It's not all that stiff. Just re-tighten the bolt a little to hold it in place. Over-tightening this bolt is as bad as loosening it too much. You can swage the taper-piece into the tensioner shaft and it makes future adjustments very difficult.
4. If you have unlatched the chain and secured the loose ends with safety wire so it doesn't drop down into the sump, you can now remove both cams and set them wherever you want. Middle of the head is as good as any. I prefer a less cluttered work area.
5. Remove the buckets, and set them somewhere in a manner where they can be replaced into the holes they came from. The shim is usually stuck to the top of the bucket, but sometimes is stuck to the valve head. Be careful that you don't carry the bucket across the open front of the engine, as this might be the moment that the shim decides to come unstuck and drop down into the depths of despair (to mix metaphors).
6. Using a dial caliper, measure the thickness of the shim. Calculate the difference in what your previous clearance was and what it needs to be. Add/subtract the difference from your existing shim to define the necessary thickness of the new shim. Select the new shim from your $600 collection of shims, and reinstall it all in reverse order.
7. Reinstall cams, but not chain, and measure new clearances. If they are all close, button it all up.
Good luck.