If your husband is into making model engines, how about a set of castings for one of the P.M range of models or a set of drawings of one of the little internal combustion engines which can be machined out of aluminum blanks, sorry I cannot remember the name of the designer. (or maybe as folks have said a tool voucher ) The finished engine, would give something nice you both could appreciate at the end of the day.
You sound a really nice lady God bless.