In response to your earlier questions yes it's a stock engine, On3 turbo kit, Tuned on 91 octane as that is the most readily available.
I mean they do make variable aspect ratio turbos, you could also use something like a twin scroll turbo/turbine housing but that could make for some interesting exhaust routing
Almost anything can be tuned, If it's available on the LT4 engine it should work on our engine. My only real concern would be the firing order and the balance. The AFM system (when mine was active and stock) seemed to cut out before any real load was applied to the engine, I can't imagine it'd be designed to run under boost in 4 cylinder mode. Could maybe be more achievable with the DFM on the newer engines however I'm not sure you'd really want to? Why build boost/power with half the engine when you've got the other 4 cylinders to give you more power. The only reason I'd want to turn my AFM back on is for the fuel efficiency when cruising down the highway. But that's primarily because I incorrectly sized my turbo so I build a little more boost cruising than I'd like. Which brings up another aspect to this, turbo compressor maps are an animal of their own (at least to somebody like me) and you'd obviously need to be quite dialed on what you choose with that.
I'm not saying this isn't achievable, but I'm not sure it'd be entirely worth the amount of effort, unless you're just doing it to say you could. If you were really dedicated to 87 octane, I'm not sure exactly but a certain company might make a higher grade of 87 than another I know shell 91 is widely regarded as the best 91 octane fuel that's readily available I'm not sure if anybody has a reputation for 87 octane. CamGTP knows considerably more than I do although I'm not sure 89 would totally reduce the engine knock, simply because 89 octane is simply a blend of 91 and 87, all of the lighter ends of the 87 would still be there just to a lesser extent. But you might know more in that regard since your studying combustion I am by no means well versed in the exact differences in octane rating as it applies to combustion nor am I an engine tuner