The Sun 3/60 was introduced in July of 1987, although mine was built in 1988. The 3/60 came with a monochrome framebuffer on the mainboard, but an optional colour frame buffer could be mounted as a daughterboard - with this optional framebuffer, you could run two monitors simultaneously (colour and monochrome). The resolutions are remarkably high for the late 1980s, either 1600x1100 or 1152x900!
The 3/60 is in a wide pizza box form factor, a desktop style where the monitor sits on the
chassis. Given the sizes and weights of the 19" Sun monitors available, the chassis construction
is robust to say the least.
The 3/60 uses it's own semi-proprietary bus connector, a P4. This bus type was used on other 3/ models - but P4 differs even amongst the 3/ line and boards are definitely not interchangeable.
Powered by a 20mHz 68020, with a 68881 FPU and a Sun-3 MMU the 3/60 was capable of 3 MIPs, and expandable up to 24MB of memory.
Like the 3/100, the 3/60 has a spot on the mainboard that looks like it could fit a 3.5" drive. In the case of the 3/60, however, this looks like considerably less of a hack and more likely an extension of Sun's intention to mount one there at one point. The mounting holes are pre-drilled in the PCB, there is the pad for a SCSI header already right there by the DE50 header, and below the battery is (obscured slightly by a capacitor) an empty four-pin pad for power. Given the 3/60 is a single board, with no boards above it, it seems quite probable that installing an internal drive here will not adversely affect anything. Why it was never deployed from Sun with one, we might never know.