Microchip PIC Development with OTP Devices (12C672)
We use the Microchip ICE2000 emulator with the appropriate module. 

These are available on eBay for a reasonable price. The processor module that you want to use for the 12c671 / 12c672 / 12ce673 / 12ce674 is PCM12XA0.  You will also need the device adapter which is part number DVA12XP081.

Generally speaking, if you purchase a used ICE2000 from eBay that comes with the proper processor module, it usually includes the device adapter as well.

The cool thing about these tools is that they have essentially a lifetime warranty.  Microchip will repair or replace them when they die - which is almost never.

FWIW - we use the 12F675 instead of the 12C671 / 12C672 for all new designs. Less expensive and contains eeprom as well as a better a/d converter.  You can debug them with the ICD2 / ICD3 / PICkit2 / PICkit3 with the appropriate debug header.  The only downside is that you get one breakpoint instead of unlimited breakpoints with the emulator.

Why do you want to use the 12C672 when better parts are now available? These new parts are pin compatible with the older parts.