The build type page http://tomatousb.org/doc:build-types states ;
"K26 builds are of two different types: MIPS**R2 builds (for older CPUs) and MIPSR1 (for newer CPUs). You must download the correct version given your router."
Isn't MIPSR2 actually for the newer CPU family, and MIPSR1 for the older CPU family ? Seems to be stated backwards on this website, as quoted above.
For reference see ; http://www.linksysinfo.org/forums/showthread.php?t=63587
"MIPSR1 (MIPS32 Release 1 CPU) builds:
Asus WL500GP v1, WL500GP v2
Asus WL520GU (4MB flash - "Lite" edition only with no JFFS and CIFS, or no-USB Std edition)
Buffalo WHR-G54S, WHR-HP-G54 (4MB flash - use no-USB Std edition only)
Linksys WRT54G-TM, WRT54-GL, WRTSL54GS, WRT300N v1"