whe you get impeller, get the kit. your motor is older and if you need parts or seals, you have them. you'll need a little outboard oil pump for the lube oil. available at a lot of auto stores for about 5 bucks. look at lower leg, you'll see 2 screws, one say fill, other vent. remove both, drain and pump in bottom till comes out vent. best to replace under screw gaskets as well.
parts available here
http://www.oldmercs.com/196869merc1000.htm