BTUs needed for a 1961 Ambassador

This seems to the simplest to make a new plentum for to adapt to what is already there.

Is 16kBTUs enough?

For $350, it seems like a steal to me and right there in my budget just above of what I wanted to spend for a used one...

Opinions?

Suburban Furnace Nt16s Series Ducted - 16,000 Btu-pplmotorhomes.com