Just about any 360 controller will do ya for the board, just depends on which one ya get as to how big a mess it'll be to get it setup in the 3 Common Line setup that Sony uses so ya can wire them together, the one 360 controller board that ya do not want to use for this is the CG one as splitting the grounds on that thing would be a real headache and just not worth it.
Most of the ones I've done have been the Black controllers, no one seems to care for the White one much.
I do on occasion make one up, but when a controller has a price tag close to what the console costs not many people get in line for that.
Just a really, and I mean really rough rundown of what goes into one of these things is..
Get the controllers, and since there are 2 versions of DS3 and 3 of the 360 controller board ya can use that changes the amount of work and what all has to be done for each combination, hence no tutorial on it.
Strip the 360 board of pretty much every component, again depends on the version of 360 board you're dealing with.
Remove the Sticks, Battery Connector and LEDs from the DS3 board, also the Daughter board Connector, but again that's board version dependent.
Rewire the 360 board to conform to the PS3 layout, this can be a real mess and again depending on what version of 360 board ya have that has to be gone about differently for each one, but they all involve cutting traces at the right spots and soldering wires in place.
Trim the Triggers from the 360 board so it will allow the PS3 board to fit in between them, this has to be done as well as the PS3 board trimmed to make it all fit.
Cut the DS3 board so it'll fit between the widened Triggers, there is a certain amount ya can take off it and not really hurt anything, any more and ya make a real mess to rebuild, too little and it's not gonna fit.
Mount the PS3 Sticks on the 360 board, bit of a mess as they aren't made to fit in there.
Wire the one to the other, this also depends on which versions of board ya have as to how it goes and takes around 20 or so wires of 30awg that are only a couple inches long for the most part and all have to be soldered to spots just about as small as the wire is. The first few aren't so bad, but once ya get about half way thru ya start to wonder.
Then the shell even has to be messed with to get the proper range back out of the Sticks and to allow everything to fit back together.
This is another reason I doubt I'll make a tutorial any time soon as each of those brief outlines leaves out a TON of details that are extremely important as well and would almost have to be done via a video tutorial or just a load of pics. This brief outline also brings up so many questions that could have anywhere from 1 to 6 answers depending on what boards you're working with, so if anyone goes getting into one of these it's a mess no matter how ya slice it.
If I had to pick out the easiest way to make one it would be the older DS3 controller and a Wired CL 360 board. Reason is the Wired CL can have the Common Line split to conform to the DS3 layout much easier than either of the Matrix boards while the older DS3 has the connector on it and after it's removed ya have access to every button on both sides of the DS3 board to wire things up, so ya can keep the wiring mess half and half on it sorta, plus the CL board has TP spots to hit for the most part and that makes wiring the 2 together a little easier.
The combination I use most times is the Wireless Matrix board and either of the DS3 boards, the new version ones here mainly as the older ones with the connector are becoming scarce.