Upgrade parts for Lionel 6-28500 Command Ready Missouri Pacific Conventional GP20??

C08 is a very good version to use for this, and yes you can use a later version of tmcc railsounds.  You just can't use legacy sound. G

@lpb007 posted:

I have 2 Lionel 6-28500 Command Ready Missouri Pacific Conventional GP20. The parts list on Lionel's website lists the following as necessary to upgrade these units to TMCC:

691R2LCC08     R2LC / RADIO RECEIVER (C08 CODE)    
691PCB104D     RAILSOUNDS POWER SUPPLY (ALT: 691RSPRA00)      
691PCB1061     RAILSOUNDS 4.0 / GENERIC DIESEL      
6108129550     COIL COUPLER / MNT B / LENGTH: 2.01"

Is there more current equipment particularly a newer version of Railsounds that could be used?

You can use RS 5.0, and sometimes you can even get the early Legacy RS 5.5 board working, that has been hit-or-miss for me.

Is the R2LC (C08 CODE) limited for use with Railsound 4.0 or can a Railsounds5, 691RS5002E, or later be used with the R2LC.

In general, I recommend the C08, but the C13 should work as well.  The C11 version had a couple of issues, I'd avoid it.  Any TMCC RS board will work with the R2LC-C08

Can a later version of the R2LC be used?

Yes.

Is the 691RSPRA00 UNIVERSAL RAILSOUNDS POWER BOARD preferrable over the 691PCB104D RAILSOUNDS POWER SUPPLY?

They're equal, not sure why they even list both of them.

Is the 691REG5A00 DC Regulator Board / 5 VOLT necessary for use with the 691RSPRA00 Universal Railsounds Power Board?

No, that's only used in specific locomotives, usually with Odyssey boards.

George and John,  Thanks for your reliable help.   Pat B.