After testing Puppy Linux has been installed on both machines and works stable and very, very fast. (The older 64MB machine required a previous creation of a swap-file/partitioning, if I recall correctly, and - as usual with Linux - the soft-modem is not working right from the start, but I don�t need it).
External PCMCIA CD-Drive: The SR1K machine boots from an external drive. Since PL 1.0.9 you need to pass this parameter at boot time: puppy ide1=0x180 nopcmcia.
Maybe this information is helpful for somebody trying to bring his/her old VAIO to life again and who is interested in Linux . I believe Puppy Linux is the best choice here today.