Check the "3rd party integration" doc. It states that the DS107e, DS107, DS108j uses a 2.4 kernel. All firmware mentions proc type in the name, but these are called "powerpc". Maybe that is the arch name. I found out the arch names (and updated the WIKI with it) by peeking into squeezecenter packages, where they are used the first time, however, there are no squeezecenter packages for those models, nor do I have one, so can't check. In some cases, packagescripts looks into /etc/synoinfo.conf, at the "unique" key. It looks like that key is made like "synology_archname_type" for instance, on my DS408: synology_ppc854x_408. So, the question what is that key on one of those powerpc models..
I really like it if Synology updates his document and explains all the things in the package file, instead us trying to decode it.
In the mean time, I would suggest "noarch", to prevent any nasty errors, in worst case, people download and install the wrong one, but the program will never start.
unpacking in different directories are possible, it is possible to configure it to have it on another directory. Can't tell you out of my head how I did this in the past, can't access my development linux server at the moment. Easiest thing to do is to get familiar with the optware trunk of NSLU2 project, there you are able to compile using different toolchains next to eachother.