There are some extremely amazing lenses out there and this Pentax-A 100mm f/2.8 SMC Macro is a prime example of mechanical and optical perfection. However this is a hard to find lens and still costs just as much as a newer auto focus 100mm macro lens even today. For perfect focus I would check Ebay to see if you can get a split focus screen for your body.
There is a huge difference optically between the Nikon 60mm f/2.8 Macro D VS. Non D although many people will try to tell you the only difference is the updated metering system for flash. Not true. I had 7 lenses on hand to try and they all told me there is also a multicoating improvement and it also seems there is a optical difference to get this diverse results.
While this Non D Nikon 60mm f/2.8 Micro AF is a fantastic lens you might want to skip it and get the newer Micro D version unless you get a really good deal. There is a difference which was very evident after shooting 7 of these lenses together.