Return T-Mobile router to T-Mobile CFE and Firmware

[Ramias]

I have the TMO Ac68U that has been running Merlin for several years.

I want to return to to T-Mobile.

It is currently on CFE Loader 1.0.2.0 and Merlin 380.66_4.

I have the original CFE.

Should I start here https://slickdeals.net/forums/showpost.php?p=73690012&postcount=3895 with Section 6 and restore the original firmware?

I also have a very old TMO firmware TM-AC1900_3.0.0.4_376_1703-g0ffdbba.trx.

Should I try to load that with my current Asus boot loader first, or after I downgrade the CFE to the original (while still running merlin). Will Merlin 380.66_4 then boot with my original TMO firmware?

Is there a better downgrade guide? I at least have the firmware (Dated Sep 23 2014) and original CFE to work with.

Thanks

 

[Ramias]

Well I took the plunge so I'll post this here for posterity.

It worked.

I thought I bricked it at first (expected to connect to it on 29.1 but instead it was on 1.1). Had to boot with reset pressed to get into CFE mode; even after flashing with CFE mini boot loader to the TMO version I had it came up on 1.1 even though I had the right firmware; reset to defaults and it came up on 29.1.