This may or may not help, but it's at least minimally informative.
There were two ADC Integra headshells. The one you posted, which will of course not fit, and one that
will fit the PF-800's arm:
View attachment 1186407
Note that the flat is on the top, but the pins and sockets all correspond. To insert, back out the setscrew nearly all the way, insert, then tighten the setscrew.
Yamaha also made a p-mount headshell for this series of turntables; I use it on my non-Yamaha straight-arm tables. This would be an ideal setup for high-quality p-mount cartridges, which are still available, though hunting may be required.