ya if ur gonna get the extended swing arm u might want to add either +1 fork leg extensions with heavy duty springs or a new set of forks to even out the ride. i have heard that alot of the 50 cal stuff isnt great quality though but i mean if ur just gonna have it for back yard fun that would be fine. also a heavy duty rear stock shock spring or a new shock would work out alot better than stock. it all depends on how much u weigh.
on the shock maybe an Elka or works...I have a Kitaco but it is a stock style replacement with a heavier spring and better internals...no adjustments other than spring preload I think...depends on what you are going to do with your bike...if you are moto crossn..I would suggest a fully adjustable..if your stuntn not so much
I would go with CHP also maybe TB (Trail Bikes)..I have a TB HD auto clutch on my kids 50 (88)..works good...got on the Ebay for about $67..I am using a CHP lite 88 kit with a E22 70 style race head (massaged by Firepower) and a DRATV domed piston..works great...from what most people say u should stay away from 50cal