Ensuring the parts are correctly fitted is only part of the battle, the real challenge lies in getting the bike running just right so it's always running at its best. There's no point fitting a load of great parts and then taking a wild stab in the dark at roller and jet settings and leaving it at that. As for 70 kits being unreliable, a cast iron twin ring 70 will be just as reliable as it's standard 50cc setup and would definitely be the first addition I'd be making along with a suitable exhaust.