This valve is indeed a complete assembly and will come with the thermopile and piezo ignitor. This should be everything that is needed to retrofit the existing valve in your fireplace.
I am currently checking the BTU capacity of the old SIT 0630516 to ensure that this is comparable to the Dexen valve. If they are similar to one another, there should not be a reason the valve could not be retrofitted to your unit.
As far as installation difficulty goes, I cannot speak to this point, as we are not a dealer of Malm fireplaces and I have little experience with how they route the thermopile/pilot leads. Depending on how far away the valve and pilot are located, longer leads may be necessary.
I have verified the the Dexen and SIT valves are indeed within 2K BTUs of each other and have similar incoming gas pressure requirements. As I mentioned, a retrofit should be able to be done.
However, I would still contact Malm to discuss the possibility of the swap, as they will have more information on what will need to be done.
Collin C. - NFI Master Hearth Professional
on February 24, 2012