Sorry just seen. Yes, I remember 8 car 2600s in action on the northern suburban in the mid 2000s though originally 4 was more common, but gangways were in use.
They weren't unknown to run in multiple with 2800s on DSER line services and again the gangways were in use.
Re: specials, Táilte did look at operating a tour taking in GVS but unfortunately resources and scheduled works precluded it this year, however we've had some nice chats with NIR people about the future...
Worth remembering the acceptance procedure for a loco to run on the mainline has taken years in some cases, it wouldn't be worth the while going through for it a one off tour (aside from all the other points).
I gave into temptation by the model devil who possessed me and added the P class to my cart. Always had a penchant for the smaller Terrier-esque locos.
On enquiring, Rails have advised me that there's no need to do anything, "the orders will be transferred automatically as they are" so sounds like a nice hassle free experience, kudos to Hattons and Rails for looking after the customer.