As others said, the SB-16 is an unusual flash because it could have either the regular (ISO) foot, or the special foot that fits over the F3 rewind knob (Each of the F, F2, F3 had an unusual flash coupler arrangement due to the exchangeable prisms).
The easiest way to do flash exposure without a flash meter or TTL is the way most people did it before TTL, which is to get a flash that has one or more "A" modes. You set the flash on "A" and, given the ISO, read the aperture off the flash for the "A" mode. For example, it says f/8, so you set f/8 on the camera, connect the PC output of the camera/lens to the flash, and the flash photocell reads the light reflected from the subject and cuts off the output when it thinks the exposure is complete. The SB-16 will do this, but so will the Vivitar 283, 285, Nikon SB-24,25,26,28, etc. These are all capable flashes that can be picked up for near nothing because they aren't TTL compatible with modern cameras.
The one thing to watch out for is that you want to do macro, and most A modes have a minimum flash-to-subject distance as well as a maximum. If you tripod mount the camera, and the min distance is say 3 feet, you can hold the flash up 3 feet away from the subject, using a pc cord to move the flash off camera. Or use the bounce feature of the flash to bounce light off a reflector. You'll generally get nicer lighting with off camera or indirect flash anyway. For more information about off camera flash and not using TTL, try reading the Strobist blog.
Thanks for this! Turns out there isn't a working SB-16 regular foot available anywhere on E-bay, and someone recommended the Vivitar with the extended sensor for macro work, so I grabbed one of those, too. I'll sort it all out and probably end up with spare parts for a camera swap at some point.
I really appreciate the points about macro shooting, which likely will be most interesting and most challenging, especially when I use extension tubes.