Charcoal absorbs bad odors. I would purchase a couple pair of the charcoal OdorEaters brand of shoe insoles and close them off together in a clean bin or closed garbage bag for a couple of weeks.
In my opinion, it is very risky to try to wash blocks (or an unquilted top) without first basting them to a foundation fabric. You can end up with a distorted mess, even if you hand wash.
You really need something that absorbs odor, not something that masks odor. My featherweight machine's case had a terrible musty smell in it. Tried a dryer sheet, tried soap -- everything seemed to just add a different odor. Fresh air and sunshine did not help enough either. The charcoal OdorEaters insoles finally did the job.