Vintage Dirt Bike Q & A

I recently purchased a 75 I think anyway mt250. It smokes white a little so I am going to replace the seals. It also dosnt move once shifted into gear guy told me the clutch plates were stuck together I think he is full of it. What would cause this I think someone put the clutch back together wrong wont the bike just take off when you kick it if the plates were stuck? I am also going to use a cr topend and rotor but was unsure if the cr crank was lighter than the mt crank or if it would even fit I asumed it was and would and am in the process of buying one. I also read somewhere that you can use some of the cr gearing in the mt tranny to give you better dirt ridding down low anyone got any info on this? Also should I let just anyone port the cylinder or can you guys recomend somebody?