Hi Tim, I've been reading your saga and you finally ask how tight the crank nut should be?
On a tapered shaft application, the nut should actually little more than hold the flywheel/ pulley or whatever in an already tightened position and would only reluctantly use the nut to do this. On a light application such as this I use a hollow brass drift which has internal diameter only slightly larger than crankshaft whereby you can safely tap the flywheel tight.
I suppose I'm lucky that as a retired farmer who did all his own mechanical work I've acquired most tools for most jobs and learnt the hard way by getting it wrong a few times which becomes expensive. For bigger applications I have various triangular plates, from 10mm thick, with a hole in centre with a stud tapped in towards each point of the triangle.
Flywheel/ pulley goes on shaft followed by plate then nut on shaft, the 3 studs are then gradually tightened and bingo it's not only tight but also true, plate comes off and nut goes on. I still has various rotovator/cultivators that I still use, one of which is a Merry Tiller Titan with most likely the same Stratton 5 hp. Believing it to be the same if you happen to progress to fitting a new carb kit, on reassembly the choke should be pulled out about 3/8 inch before assembly. Sorry to be longwinded, but as Geewiz said it's difficult without photos. If the taper happened to be slightly worn/ damaged on jobs involving much more torque than this, and larger, I have had 100% lasting sucess using Loctite bearing fit. Hope everything goes well, I know the feeling when you've aquired something and it goes wrong before you've used it in anger! My OH has slightly stronger views at that time and I keep my head well down!!
Regards Frank