This morning I happened to find the best pictures I've ever seen of an SU-100's interior. If there's anything out there even 1/10th this good, I've certainly not seen it.
Check it out. It's on the ArmchairGeneral site and is a set of pics showing an SU-100 restoration...
http://rkkaww2.armchairgeneral.com/galleries/SP_guns/SU_100_int.htm
Here are some samples (the originals are much larger)...




Enjoy!