I do own a Fluke 87 I think the part you are looking for is called an inductive pickup probe. I priced them out and they want around $50 for one. They only work with their model 78 automotive meter. (PN RPM80)
I'm not exactly sure how you would use a inductive probe with a standard DVM but I'm thinking you would need to set the DVM to hertz and it would show a measurement of cycles per second. You would then have to divide the reading you get by 60to give you the actual rpm (revolutions per minute) reading.
Found this little tach for $22. online here are the specs.
Code:
PT15 Tachometer
Sparks once per rev
Large 7 segment LCD display
Low cost and small size
No power required
Solid state electronics
Quartz crystal
Wide operating temperature range
High reliability
Standard is resettable, non reset version is available from factory
Indicates operation in RPMs and hours
Self programmable or factory set 1, 2, 4, cycle engine, or hour meter only
Easy to install.
Made in the U.S.A.
http://www.enmco.com/