I highly doubt you'll get 700lm. Using 3C in a 2D maglite only requires you cut a piece of 1" PVC to length and modifying the spring. Pretty simple. Here's the tailcap from one of my 3D maglites. I've also seen others where the spring was turn upside down and even cut down and recessed in the bottom of the tailcap after the anodizing had been removed.
The mod is simple. You dont have to work on the switch unless you just want to lower the resistance for slightly higher output. Alkaline cells are really just not up to the task of powering an LED like this. On 3 C alks at the 1 second mark it will be high, but by about the 30 second mark your going to be looking at around 400 ish lumens is my guess.
The only XML mags I ever sold that the buyer had strict intentions of running on alks were a 4 and 6 D cell. Even 3 D cell alks would only power it to about 2-2.3A if I recall right.
This is just my opinion but when you do get your NIMH cells I suggest saving a few extra dollars to get a good set. It makes a difference. My personal favorite are the Accupower LSD C cells. I have driven lights to 13+ amps on 3 of these. They carry a load well, and they are always charged when you come back to them. About the only draw back is you have to buy them in a 2 pack.
In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not. Shorty C/D M*glites