Lennox 61M35 Drain Trap

Does this part replace Lennox part nmbr 78L3201?

Yes it does.

i need only the small rubber caps for the drain. can you supply separately?

50M18 is the Ring, Cap, & Plug for 61M35, please check here if this is what you are looking for: https://www.gsistore.com/products/50m18