Mount your sprockets then put the chain on and measure where you want to cut it. Use the original chain. Grind off the oputside of the rivet pin and drive it out with a punch and a hammer on the vice. A bit of a POA but no biggie. Measure twice, cut once.
The strainer is a big (22mm?) bolt in front of the shift lever. You'd never figure it out until someone pointed it out. You are supposed to check it once an oil change, but I never found anything there, but it's easy and free to check so no harm there. If there was crud, I'd wash it with carb or brake cleaner. Watch your eyes.
You can make a gasket easy. Pull the bowl and coat the lip with grease. Make an imprint of the bowl surface by pushing the grease on a piece of gasket material. Whip out your knife and cut it out. It's Colorforms fun.
(Don't know if you are old enough to get that joke).
Bill