Originally Posted by: boxcab 
Uh....been watching for a responses for 5 days...
I can't find these cars or parts "nowheres".
Any suggestions regarding where the heck we can get the parts for US conversions?
Out of desperation for more "US" rolling stock, I just considered hacking into a M-made 4 wheel-truck green-colored "Texaco" car I have...she may be a victim.
I feel sorry for the poor little thing: she never did nobody wrong. She's quivering, knowing the ax is getting ready to fall.
I may wait 'till after the hunting season. Maybe a savior will arrive.
Anyone?
Regards,
Boxcab
Hello Boxcab
Maybe your question is too vague...so it is hard to give you a useful answer.
I did a lot of conversions when I was still living in California running a Märklin Service Station, so I can tell you it is hard to give a "one size fits all" answer!
I could have given you the name of my successor, but unfortunately, the nice man passed away a couple of months ago.
There are two things to consider when modifying to run US type rolling stock to Märklin 3-rail: wheels and couplers
For couplers, I solved the problem "backwards"

: it is relatively simple to find conversion parts to Kadee couplers for most US brands
I just then used NEM pocket Kadee units on my US locos (Big Boy, Alco PA, Mikado, etc..)
The second problem, the wheels, is (much) more complicated!
Two problems here: wheels' spacing and flange depth
Marklin flanges are deeper, most US flanges will not provide reliable operation on switches, etc.
Spacing (measured inside the flanges is 13.8 mm for Märklin, 14.2 mm for 2 rail equipement.
You can try to simply reduce spacing on the original wheelsets
Tools to this purpose can be found at NWSL (
www.NWSL.com).
But in most case , the only solution is to replace the wheelsets or the whole bogies with Märklin's.
This however may need a little patience, I have no idea how well Walthers has the spare parts supply organised.
Your best move may be to join ETE (www.ete.org) where you'll find a lot of same minded people
Sorry that I couldn't help you with more specifics.