I have done a few of these upgrades - what is different is the metal frame, the fan(M6497 has four blades), the heat sink, the modem card and the metal pan where the airport card sits. The modem card has a different hole pattern for the screws (which I never install now) and the pan can be easily bent on one corner to fit the new fan but all the parts are easily found on ebay for cheap. One thing that can't be changed is the reset button - located on the left side on the M6497's it is on the back on the A1005's. The pins are next to the fan on the new boards, if you want to have access to the reset button the best way is to extend the wires to the old position. Last thing I can think of, there are a few screws/holes that are different so don't drive yourself crazy if you have an extra screw or are short one.
You changed two things and the computer works, but you can't say with certainty which one was causing the problem. There are a lot of people out there who don't have extra displays with inverters to fix their problem. I'm sure it doesn't matter to you since your computer it running, but I don't understand why you don't think it could be the inverter since they go bad much more often than panels do. If they fail the computer will still start with no light, but if it shorts it won't.
forget the power supply right now, check the dc/dc board, if you don't have the proper voltages there then ck the power supply. looking straight into the dc/dc female plug... onA - Grd-12vR -(?) -5.0vR -3.3vR (?) - 12v - 12v - 5.0v - onB - 3.3v the ? pins are probably grounds as well, but I'm not 100% sure - the 'R' voltages are only on when the power A and B pins are touched together ie. the computer is on
I'm jealous, I can't get the first LED to light on my 17". from what I have learned so far the I mac runs on three voltages - 5v, 3.3v and 12v for the inverters. If any of these are shorted out (go to ground) then the iMac shuts the power off. So you probably have a bad inverter or bad bulbs not a power supply problem.
My personal opinion is that there is something wrong with the LCD's inverter. I know if there is a short in any power supply the computer will shut down. The iMac runs on 5 and 3.3v but also has 12v fed through the Logic Board to the inverters. So if you have a shorted inverter it wont start up. You have a problem with the inverter or the video. And a connector for each one so you can unplug the power to the inverter on the logic board but leave the video connector in and if it starts up you have a bad inverter.