I run the O'Donnel purple plugs, cheap and they have always worked great and lasted forever for me.
If I remember correctly you can get the OS in both a short and an SG crank, but I know either way you can drop it in.  I used a bump box on mine so I had to order a specific flywheel but you may be able to just use your stock stuff.  I can't remember if the only the SG crank comes in pull start and the short as a bump or vice/versa, it's been a little while since I dealt with this.
It definitely is a night and day difference between the motors, especially if you add in the 2 speed. It's like a whone different car in my opinion.
Of course then you will start to destroy your stock diffs and want to upgrade those to the HD ones...  You know how it goes.