Thanks for all of your reposnses. The PPW kits are a bit pricey, especially compared to the Micro Mark kit offering similar components on sale for $27. I just might try the Micro Mark kit. I promise to post whatever results it yields.
I have tried a couple of the Micromark kits and they were quite satisfactory. The motor is quiet and smooth running and has about the same rpm as the Mashima/A-Line. For $27 it’s a bargain.
Aside from using the decoder in the link from my previous message, which only requires switching out the motor mounts and the brush plates, everything else is just plug and play. Athearn does sell this Genesis conversion motor with DDC board attached. It may fit in a foru axle, but I know it will fit a 6 axle.
http://www.athearn.com/Products/Default.aspx?ProdID=ATHG63839
Here is a link to a forum thread about motor replacement for the older athern blue box engines. It is http://cs.trains.com/mrr/f/88/p/191616/2092409.aspx#2092409 i hope it helps.
Go to this link below and you will find at least four different motors Athearn offers in their parts list, I would guess at least two of them, maybe all, could be used in blue box loco’s.
http://www.athearn.com/Search/Default.aspx?CatId=THCR&PageSize=72
Check it out.
Cheers, Jim
I’m reading this because I too am thinking about upgrading an old BB loco (but in my case the scale width hood GP38-2). Good info here, nice to hear personal results (I had no idea Micro Mark motors ran slower than others).
One point I’d like to clarify is the ‘worse case’ amperage draw. It’s not when the wheels are spinning and the loco isn’t moving, it’s when full current is applied and the motor is locked so it won’t turn. To measure this, you’d have to stick something into the drivetrain or motor to keep it from spinning and give it full throttle…but only briefly. I don’t know how long it’d take to burn out a motor, but if you left it on and walked away, you might damage the motor (windings or commutator). Maybe these motors are robust enough to not burn out, but I don’t want to try. 
Sorry if any of this is wrong (please correct me if it is!) or if this is all old news to everyone. I just wanted to clarify how to measure max current draw.
Also, I used a digitrax (DH123?) in an old BB GP35 and the decoder worked fine. The loco didn’t move until speed step 20 or so…but I think that’s the age of the old BB loco, not the decoder (I’ve had that loco for 20+ years and put a lot of miles on it). I’ll have to pull the GP38-2 out and see how to runs on DC before I install a decoder (but I think since it’s a newer BB it might have a different/more suitable for DCC motor in it?). I’ll keep an eye out for more info/results on this subject…let us know how your repowering worked out for you (and what motor you used).
I used a Micro Mart Motor to repower my BB u-boat
I also bought their universal coupling kit
http://www.micromark.com/universal-coupling-kit,9637.html
and have used it on other installs
I did Cut off the Capacitors on the motor
Since they are required in the UK
but they are not needed here in the US
and i was told they can cause problems with DCC