There are the typical components involved here. In the second piture I marked the additional components that had been missing.

With the new BIOS all Intel and AMD DX4 and Cyrix CPUs can be used. I will try an AMD DX5 - 133 MHz next week. I hope to also have the two video RAM chips available until then.

Here´s an overview of the board in it´s current state:

Several limitations have been solved, I wish I had the original ISA-VLB riser card for this mainboard to be able add a network card or VLB graphics.

I had never seen a 486 board before, that had support for a switching CPU voltage regulator, pretty cool!

Several FIC 486 mainboards had switching regulators. Later, when CPUs demanded more power, they switched to linear regulators with bigger heatsinks just to return to switching regulators on the socket 7 boards to provide the even higher power for Pentium (MMX) K6-2 and K6-3 processors.

Today I equipped this 486-GACV with a AMD "X5-133AWD":

Double RAS SIMMS must to be placed in slots "SIM3" and "SIM4" here.
You can also see the jumpering here: Array RC1 must be populated, jumper "JC6" needs to be set to "2-3" (multi x2) to operate at 4 x 33 MHz.
BIOS version "3276 gn1" supports and correctly identifies this processor unlike earlier versions. Write Back L1 cache is enabled correctly.

I´m still waiting for the additional 1MB video RAM to arrive...

I have the same board but it was complete from factory.
I was thinking in using the same CPU as you, but I don't know yet if it provides the required voltage.
Can you take photos of the VRM area as you have it and the jumpers all over the board?
Would be very helpfull.

It´s all in this thread.
You can see all the general jumpering on my "8GACV.jpg" picture above.
The complete jumpering for the AM5x86 - 133 CPU can be seen in picture "GACV133.jpg" above.

The output voltage of the VRM circuit is determined by the resistors R68 and R69 alone. For R69 = 2K and R68 = 3.6K you get around 3.4V output.
In the datasheet for the "2576T-ADJ" you find the formula for calculating the resistors for any alternative voltage in case you need it.

And don´t forget to flash the latest BIOS version "3276 gn1" for AM5x86 for enabling write back L1 cache.

Thank you, that adicional information about the resistors is great.
The BIOS, I already flashed the last one, but the CPU isn't always correctly detected, even with the original. It have a Intel DX4 66, but most of the times it is detected as "Unknown 60Mhz", 75 or even 80. I don't know what is the issue with that...

The jumpering must be 100% accurate to make sure DX4 or 5x86 CPUs are detected correctly.

Sorry, It is a Intel DX2 66. The board/bios don't detect it most of the time, and is 100% as it should be configured... A friend said something about a cristal not working right, but I'm in the dark about that...
I have access to the same CPU you have, I'll give that a try this next week...

Both DX2 / 66 and AM5x86 / 133 need 33MHz oscillator frequency. Ii is set by jumpers JK1-JK4. If the frequency is unstable (with the 5x86 as well) the oscillator circuit or the crystal could be the culprit.

You will also need the jumper array "RC1" that isn´t needed for DX2. Sometimes it´s missing if the booard was originally equipped with a DX CPU.

Ok, so this could be a good help, if the AM5x86 133 is not identified as it should, the cristal could be bad...
My board is from a AIO, a Fujistu ICL PCTV that I'm trying to restore and make a bit bether. The original CPU was a IBM Blue Lightning 66Mhz, installed a Intel DX2 66Mhz and even flashed a new bios to see if the CPU was correctly detected, but those 2 CPUs both are identified as whatever it feels like...
I have to confirm the VRM voltage and see if I receive the new CPU by friday so I can test it all...

The R68 and R69, do you mean R66 and R69? Those are the ones on the VRM area...

And I have a jumper in CN11, I see ypu have headers but no jumper...