LOL, this in the internet so usual caveats apply If this was a finanace website i would say something like "do your own reearch "
SO I am talking out my ass as most know, but i think you will find why he has the -5s in the first instance is that the engine builder/tuner has had more success with the -5s then the 2530s. There are a few in the Vic club that have gone from 2530s to -5s, some because they wanted to go tarmac rallying, others because it was seen as an upgrade...though they do concede that the -5w make less power, in Vic anyway there is a trend to use the -5 as they are better for track work. (on 2.6Ls anyway)
So, take that with a grain of salt as the above is just an obersvation, and perhaps i am reading too much into the fact that this build uses -5s in the first instance. After spending all that cash on 2.8L, V-Cam, brakes etc etc i would be surprised if it wasnt a concious decision to use the -5s.