NJRoadfan has it right on the nose.
But the 550c and the 540c should be similar enough to work on the same OS (according to the technical notes I seen). But System enablers were for System 7 and in 7.6.1 should have ended their use as Apple promised then "No More System Enablers" in System 7.6+. But from System 7.6.1 to OS 8. Thus OS 8 can boot from some 030 macs, most 040 macs and all of the PowerPC Macs of the time without enablers.
@NJRoadfan - All, at least all 68K, Macs start with their ROMs at $00000000 and then there is some electronics Voodoo to bit-flip the ROM's addresses in hardware to just above $40000000 or $80000000 (depending on system) and start the system from there. There's no actual moving of the ROM other than shifting its hardware address registers, and then it opens up memory at $00000000 and clears and counts the RAM from there. That has been some serious Apple Voodoo secret for the longest, but we think we can figure out how its done in hardware. In software its easy, in hardware it gets tricky.
But the 550c and the 540c should be similar enough to work on the same OS (according to the technical notes I seen). But System enablers were for System 7 and in 7.6.1 should have ended their use as Apple promised then "No More System Enablers" in System 7.6+. But from System 7.6.1 to OS 8. Thus OS 8 can boot from some 030 macs, most 040 macs and all of the PowerPC Macs of the time without enablers.
@NJRoadfan - All, at least all 68K, Macs start with their ROMs at $00000000 and then there is some electronics Voodoo to bit-flip the ROM's addresses in hardware to just above $40000000 or $80000000 (depending on system) and start the system from there. There's no actual moving of the ROM other than shifting its hardware address registers, and then it opens up memory at $00000000 and clears and counts the RAM from there. That has been some serious Apple Voodoo secret for the longest, but we think we can figure out how its done in hardware. In software its easy, in hardware it gets tricky.