I confirmed the LS4 crank snout is shorter, nothing that can't be done to a regular LS crank though. The single belt is basically where the AC belt is on the pic you show. It migh tbe tight, but it might clear the body. The MR2 PS pum pis not a bad option though, I've seen it used before. I think the Fiero had a electric PS pump too, I assume for the same reasons. FWIW, putting the pump in the back for added capacity only buys you time before it overheats, it will still overheat if there is a thermal issue. I don't know how much open- tracking you plan to do, but IMO, keeping the PS fluid from travelling from the front of the car to the back is one of the benefits of an EPS setup. Adding a steering cooler up front would probably be a simpler, effective solution if the need arises.
Regarding the engine harness, power to the vehicle and cluster communication, most of it is simpler than you think.
If you want the stock cluster to work with the LS engine, the coolant temp and oil pressure senders are relatively easy to adapt. There are several options to go there, depending on the OEM porsche senders, and what they used for threads. The engine harness only needs power, and a sub-fuse panel to run all of that is relatively simple. YOu only need about 6-7 fuses and 2 relays to run an LS engine. Powering the vehicle is as easy as tapping the old alternator power lead, and hooking it up to whatever generator you decide to use. I helped a friend of mine built a LT1 87 944 many years ago, the wiring was not bad at all. IIRC, he had Renegade do the cluster mods to get the tach to read right. The rest of the Renegade kit was pretty decent, he did not have to mod or tweak anything to get their parts to work right. Based on that, I would recommend them. I have 2 EFI LS swaps under my belt too, the third one is running a carb now, but is going EFI this winter. Wiring is relatively easy..

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Wiring is actually pretty straightforward once you get the motor in the car.