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Two of the chips (ROMS) share the same pinouts, the third is the RAM chip that has a different backup power supply connection. Or it could be two RAMS and one ROM. The two common pinout chips can be swapped, the other can't. I don't have a 34C handy to say which chips are which though.
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Pin 8 of the memory chips in the Spice series is the power supply pin.
The top location is wired sepearately back to the PSU module. On -E models, this connection is linked to the main power line in the PSU module, so all 3 locations are equivalent. On the -C models (includign the HP34C), the PSU module contains an extra couple of diodes and a resistor to provide a 'continuous' supply to the top IC location, to maintain the contents of the RAM.
If you get the ICs in the wrong places, then the machine should work, but you'll lose the contents of memory when you turn it off.
In all cases, pin 1 (notched end) of the IC points towards the display (this applies to the 40 pin CPU chip also).