When I created my BOM these corners came with two low profile M5 screws. I'll take a look at the BOM.

 

Looks great, thanks for updating and contributing!

 

I've added your additions into an assembly zip file with the pdf and pics. This way they won't get lost in the discussion forum and others will find them easier. I'll update it if you have more to add or updates to make.

 

You definitely won't be able to use the same offset I did with the 16 tooth pulley's, as the diameter of the 20 tooth will be larger. It will also create a slight misalignement with the idlers on the front side of the XY/H bar moving bracket. Ideally this means a redesign using M4 or M5 flanged bearings for idlers, whichever is closest to a 20 tooth pulley effective diameter. For demo purposes you should be able to get away with out a redesign, just make sure you pretension your belts in the right position.
So to answer your question... for a 16 tooth pulley the motor shaft is centered 12mm from the center of the extrusion. See horrible snipit below. The motor shaft center will have to be centered about an extra 1.4mm away, giving priority to the GT2 belt running through the length of extrusion to avoid scrapping.

 

Are you going to use an 18 or 20 tooth pulley?
Approximately:
20=13.4mm
18=12.7mm
If you are using the 18 tooth, I did a visual check and there should be enough room in the extrusion to accomodate a 0.7mm shift so you don't need to bother modifying if you don't want to.

 

Yes, was making an update last night and forgot to reload. Posted.

 

Dual extrusion finally achieved! Still needs some tweaking in the nozzle realtive position settings, but not bad for second print.

 

Yeah, in my experience I've found rip off hotends are not worth the frustration. I've had fake J-heads and an E3D v5.

 

This was done with slic3r and it is an ooze wall. Different than a purge wall in that it takes the deactivating hotend outside the wall, drops its temp based on an configurable offset, and then heats the other. You want to have tuned P&IDs on you hotends or this is a slow process. There are other settings I have yet to play with, still experimenting.
I actually used a temp offset of zero for this print (-5 is the default). So basically this was done with 7mm retraction, 0.5mm extra on reactivation, and a full height brim as a scrapping wall.

 

Yeah, the V5 I had was an Ebay clone. Probably would of been fine with ABS, but I was using it with PLA and it would jam constantly. I print 95% in PLA. I broke the heat break trying to unclog it once (my fault it broke), ordered a replacement heat break but a month and a half later it never arrived. Gave up on it.
I then got a pico hotend off kickstarter. I can get my best quality prints with it, however, it is still bad with PLA (jam prone) and must be oil seasoned. Too annoying and risky for long prints. I still have it and it will be useful for doing really high temp stuff one day.
With the genuine V6 E3D bowden style the PTFE tubing goes deep in the body, much like a J-head. No oil seasoning needed. Only ever jammed when I used 10mm retraction (for inactive dual extrusion just the other day actually).
J-heads are tried and true. I have had two fakes and two genuines. Both fakes failed due to liner issues and me trying to fix them. I lost one genuine to an overheat event that melted the peek. The other is still going strong on my other printer. Most people complain about J-heads due to leaks and that the peek melt temp is only just above what you print at for ABS.

Some factors of the nozzle design that affect print quality are nozzle tip design and back pressure. The pico has a great tip for layer control and precision, but doesn't produce as nice infill since it is so sharp. The E3D and J-head have a flat the is good for infill and wider extrusion widths, but isn't as sharp at corners and very small features.
Others factors are external that you can control such as print temperature and speed. Cooler will temps will give you better overhang angle and feature sharpness, but higher temps give better layer strength. Personally, I think I am printing too hot right now and need to back off (PLA at 212 after first layer). That said, temps can't be compared between different nozzles due to thermistor locations and other stuff.

 

I renamed the file "XY Bar Moving Ends" so hope that helps a bit.

 

Mine is supported by the base frame. I didn't share mine as they wont be the right size for anyone. When creating the extrusions lengths part of the BOM sheet I did some length optimizing plus mine have a mount built in for my relay switch for the heated bed.
As adam said, check out Thingiverse frist. If you can't find anything there and can't CAD, let me know and I'll modify mine to work for you.