I think it shouldn't be that bad. Trent will probably advice to use field ecu harness. same plugs on both sides, just with wires, makes for a neat install.
But damn I would really like to hear one thing: I've done it it was hard but doable ))) And it works ! lol.
What we get with s1 stagea is all r33 gear. and r34-type ecu plug. So if you rewire the plug to connect to r34 ecu, make it work with tps/cas/acc, you should be able to fire up the engine.
Btw. This stagea engine got a pink label AFM. Like S2 R33s and R34 NEOs. Freak engine.