I have always wanted a functional socket 4 machine and years ago (in 2016) bought IBM socket 4 board along with 60 MHz gold top Pentium P5. Didn't come with a riser (huge bummer) and back then did not know the tricks IBM had done with PSU. There were regular AT ones and with regular AT PSU board obviously did not POST.
Thought the board was defective and also Tiido gave a look but found nothing wrong but did not get it to work either.

Then around two months ago I accidentally stumbled across IBM PSU chat and thought of trying the method myself (=shorting power button pins and applying GND and +5v to PSU side connector) and voilaa! It worked. BIOS was Swedish, no big deal, spent some time trying various RAM configurations and settled for 2x32MB as it did not like 4x sticks (tried with one bank double-sided and other single sided etc, no dice).

Then tried to boot from floppy, HDD etc. Did not recognise HDD's and while tried to boot from floppy, it didn't. It did see CDROM in BIOS though. Thought the board was defective and was about to give up. Few days passed and while messing with my Aptiva it seemed the riser connector was identical to P60 board, decided to verify ground and supply voltage connections. All seemded good, checked some photos online and it seemed fine.
Connected HDD, Gotek with latest BIOS image etc and turned it on. To be honest I did not expect much but to my surprise it started to update BIOS and of course recognised HDD etc.
No idea why it would be acting that way as I did not find a single trace from 3.3v connector on the riser going to planar. Also riser is passive, there are no IC's or switches. Go figure.

Then it was time to find a proper case for it. Since PC330-P60 ones are extremely rare I just wanted some PC330 case and use that, ignoring the last number.

Just few ago I got a reply to my ad from a local who offered me PC330-75 for just 30 euros. It was a working machine but was missing a sliding door. Took it, swapped my P60 planar to that casing.

When taking a closer look at the board I noticed there were unpopulated jumper pads near CPUand silkscreened markings 60/66 MHz. Decided to solder them on and the CPU now works at 66 MHz (now 50 MHz, 60 MHz and 66 MHz are available). BIOS still shows 60 MHz but Everest verified it is running at 66 MHz and benchmarks also clearly show improvements.
For expansion I put in SB 16 PnP, A-Trend Voodoo Graphics and AIMS Lab ISA FM tuner card. No real purpose on the latter other than having one in my work computer back in 1998 and loved it.
Installed Aptiva recovery of Windows 95c on the 3.2 GB HDD (2.1 GB and 1 GB partitions), working very nicely.