Is what you are hunting for? pic is of LCR METER XJW01, PCB REV: 1.1, LCR V3.0, DATE: 2014/05/18, an all through-hole version.
There have been many XJW01 circuit, PCB and firmware changes that are nearly impossible to track, all kept close to their countrymen. If only there was rhyme or reason to the revision numbers.
Building an older through-hole rev would be risky because it misses updates. I haven't found firmware and matching pcb/Gerbers for the versions.
That V5.5PCB file has PCB111111.PCB (twice) which is a mix of SMT and through-hole, all the buttons and LEDs are in a line, no keypad PCB, silkscreen "XJW01, Putian Program REV: 5.5, LCR Meter Rev:5.5, DATE: 2016/11/27, QQ:898838627" It's in Protel PCB format Version=3.00
I have the schematic for the SMT version sold today, AUTO LCR METER XJW01, PCB REV: 1.1, CIRCUIT REV: 3.1, DATE: 2017/03/28. The circuit is similar to the previous rev's and still has a few mods, but still limited to 7.8kHz
STC12C5A60S2 has some strong claims "executes instructions in 1~6 clock cycles (about 6~7 times the rate of a standard 8051 device)."
"Operating frequency range: 0- 35MHz, is equivalent to standard 8051:0~420MHz". 1KB RAM, up to 62KB FLASH. But it tops out at 7.8kHz in the LCR meter.
I figure the STM32/DDS version has more code space and speed.