All machines of the rp series (rp24xx, rp 34xx, rp44xx, rp54xx, rp74xx) are all 64-bit ONLY machines.
To see what bitness is running:
# getconf KERNEL_BITS
It will return 32 or 64, which indicates 32-bit or 64-bit HP-UX.
getconf HW_CPU_SUPP_BITS
# file /stand/vmunix
/stand/vmunix: ELF-64 executable object file – PA-RISC 2.0 (LP64)
Here it tells you 64Bit and CPU arcitecture.