Clutch ,crank pulley, timing gear, wires, and flywheel are all SOHC specific. Throttle body for DOHC fits DOHC manifold and SOHC fits SOHC, since DOHC has a wider diameter. You'd have to see into having the manifold opening made wider to fit a DOHC throttlebody. Now as for both DOHC manifold and throttlebody transfered to SOHC block, I think the gains would be minimal.
Not sure, but I think SOHC and DOHC exhaust stuff is all the same. Even so I'd go for some SOHC headers anyway.
Suspension I don't know that much about. But really, everyone will just tell you, like I will, to just maintain your SOHC and save for a RT/TT or VR4.
