Regency ci2600 digital cat monitor

[ill_make_you_famous]

I just picked up what I believe to be a ci2600 yesterday off the marketplace for $275. I’ve been reading through the two big threads and will continue to do so but upon looking at the owners manual as well as the threads, I see that I don’t have what the manual shows for where the probe goes. The manual shows two bolts that need to be removed but I do not have that, all I have is what the picture shows, punch out? Would this be an older model 2600 maybe? Also, how necessary is it to buy a probe for it if it’s an option? Could I run it efficiently without? This will be for supplemental heat. Thanks in advance.