[coreboot] Proper way to obtain mrc.bin for thinkpad t440p?

[yk]

To anyone who has corebooted a t440p:

I followed the instructions here
https://doc.coreboot.org/northbridge/intel/haswell/mrc.bin.html to
obtain an mrc.bin for the t440p, but it seems like these instructions
are generalized and are meant for chromebooks, and not thinkpads. I
gave it a try anyways and my t440p beeps and flashes LED's (as
configured in .config, to do so on fatal error). Months of searching,
and I can't find any documentation or archived emails from this
mailing list for obtaining an mrc.bin specifically for the t440p.

There exists this tutorial https://0xcb.dev/lenovo-t440p-coreboot/ but
it tells me to use a forked version of coreboot which seems really
fishy. I browsed the commits from that fork and I couldn't find anything
that "automates obtaining mrc.bin" as it promises.

What is the proper way to obtain the mrc.bin and configure for t440p?

CONFIG_DCACHE_RAM_MRC_VAR_SIZE=0x30000 <-- also what should this value
be if the mrc.bin is 186K?