1989 blaster

I have a 1989 blaster and a 2006 blaster. The 89 doesn't have an air box, the 06 does have an air box. I was using a little k&n filter (if someone could help me find the one I was using that would be awesome) but it fell off while riding a while ago. It has the stock mikuni carburetor. The 2006...

After draining out my gear oil how much do I put back in ? And what oil would u recommend thanks