First of all, the ROM itself is fine. The stuff it contains does not provision (and is not capable of provisioning) the phone part of your 6700 for a carrier. You have to do that part manually. See this thread for what you need to do:
http://www.howardforums.com/showthread.php?t=1129718
Yes you will need your MSL. There are several ways to get it but the easiest (available only in the last few weeks) is an application someone in the titan/mogul forum wrote. You will find it in this post:
http://www.ppcgeeks.com/help-unlocki...,60.html#66905
You need to copy two files over to your device--the app itself (use the version marked 2003) and the dll file. It doesn't matter where you put them on the device, anywhere is fine. Then run the app. In the top box you need to fill in your ESN HEX, which is the shortest of the three serial numbers printed on the barcode label under the battery... it's clearly marked ESN HEX and should be eight digits long--capitalize the letters like this:
12345ABC
Then click the button. If you did everything right then six digit number in the second box is your MSL. Use that to follow the instructions given in that hofo post and you should be good to go
Note that if the ##PST (talk) doesn't work, try ##PST#.