So I have an older (1915), wood framed house. The basement is only about 5'6" high in most areas and walls are stone.
Someone did pour a concrete floor at some point but it is rustic, shall we say.

For this, and other reasons, I don't feel comfortable building a rocketmass heater in presently.

I was thinking about composting in the basement over the winter to augment our heating, and perhaps even building a small room to act as a chimney of sorts to direct the heat to the upper levels of the house.
(I sort of want the basement to stay cool to keep veggies)

Anyone doing anything similar or have suggestions or can point me to plans?

guess i should have read a bit more ... never mind ... :) https://permies.com/t/43035/Heat-house-Compost

Hi James;   Interesting idea about composting indoors for heat. Won't there be a smell?  
Central N.Y. state gets plenty cold.  Your basement is not a good location for a RMH anyway.
Consider a small batchbox brick bell heater, that is located where you spend your time in the evenings.
They can be built small , no need for a long low mass. A brick bell release's heat for hours and has a small footprint.
Check out matt Walkers tiny house cookstove heater.    https://permies.com/t/71700/Tiny-House-Cook-Stove-Heater

In the other thread, Joseph Lofthouse said that compost in his greenhouse created a lot of mould, which isn't surprising.  It won't be as bad as a grow-op, but you'll likely get mould throughout your house.

From a practical standpoint, shovelling out the completed compost would be a huge task.