There is a BIOS that supports the Plus series CPU for this board here: http://www.steunebrink.info/k6plus.htm
As you have the 1.04 version of the board, that's all you have to do. Phil had a video that shows the performance difference. It's noticeable, but it's still a K6-2, so you can't expect miracles. We have a thread here detailing how a K6-2+ 570 (well, almost any K6-2+, but the 570 is pretty affordable) can be modified to get the full 256k L2 cache rather than just the 128k if that might interest you.

SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod

https://www.youtube.com/watch?v=A2Oymnq5DEQ

Will this k6 III+ work at 550mhz https://www.cpu-world.com/CPUs/K6-III/AMD-K6- … %2B-550ACR.html

on my asus p5a-b rev 1.04?

Do not know but am not a fan of K6-iii but big fan of K6-ii. Too many quirks even if you get the board to run it even IF it was designed for it.... just MHO

This would be the jumpering für 550 MHZ ( 5.5 x 100 MHz):

Chances are good you can run it at 600 MHZ (2 x 100 MHz, seen as 6 x 100 MHz by the CPU)

I have now installed this K6 III+ 550 MHz processor https://www.cpu-world.com/CPUs/K6-III/AMD-K6- … %2B-550ACR.html and it worked fine without any BIOS adjustments. I was also able to overclock it to 600MHZ by setting the multiplier to 6 and the L2 cache of 256kb made everything about 10 to 20 percent faster. Thanks for your help.