I guess one of the biggest things is what colour is the Twin.You really don't have to worry out a timing issue as the 2 cylinders fire at the same time and for memory I don't think it is adjustable,I'll have to check that.As bigted said no replacement rings at all.You should be able to see the rings through the exhaust port.Most problems with rings occur in that area first.If you have a vacuum leak in the hoses or decompressor values that could also be a problem with starting.I only ever pull engines apart if it is the only and last resort.One of my twins had broken rings and a huge chunk missing from the top of the piston and still ran.I thought it only had a vacuum leak but after changing everything 3 times I pulled it apart.So that goes to show that even with big problems they can still run.
Also you have to remember 2 stroke engines don't really produce a lot of compression until they start running.They don't need a lot to start.Try something like start you bastard or Aerostart.My theory is if an engine won't fire on that there a problem.
