Every center is different about what constitutes an "acceptable" donor, and yes, to some, the discrepancy in your sizes would matter. But in the event your center does think you're too small, then as someone has already pointed out, you could investigate paired exchanges. One of the centers we work with used to have a policy that the donor couldn't be more than six inches shorter than the recipient, because they thought that the shorter/smaller person's kidney wouldn't function as well. They have since dropped that requirement, and if your creatinine clearance is good and you're healthy, I'll bet most centers would accept you as a donor for your husband. Best of luck to you either way.
Laurie Reece
Alliance for Paired Donation