I'm in the process of swapping a '91 HO into my '87. I have the motor in the car and the mounts bolted down, but that's as far as I've gotten so far. Nothing's hooked up, and the drivetrain is sitting in the trunk
I'm debating now (a little late) if I should swap over the Renix manifolds or not. It would probably make the conversion a lot easier, but since the motor is already in with the HO manifolds I'll probably just run with it.
So far, the differences I see are as follows:
1) Renix EGR system doesn't carry over, so I'll just do without that
2) O2 sensor was in the manifold, and the Renix manifold exits at a different angle. I'll probably have to make a downpipe and weld an O2 bung into it, possibly lengthening the wires on the sensor as well.
3) The HO fuel lines are different, both on the front of the rail. Renix has a fuel line on the front and another on the back. I'll have to either use the Renix fuel rail (which won't bolt to the HO manifold), or make fuel lines to go into the HO rail. Haven't decided which route I'm gonna take yet.
4) Rubber intake tube. Renix and HO are different, have to use the HO tube with the HO throttle body.
5) Throttle cable. Haven't tried to hook it up yet, but I'm not sure if it will work. Renix has a hinge on the manifold with some throttle linkage, but I don't care about keeping the cruise control. If necessary, I'll have to get a 91-96 throttle cable I guess.
6) Crankshaft position sensor and flex plate/flywheel will have to be reused from the Renix setup.
7) I've read a few places about differences in the Throttle Position Sensor. This is probably more important for those with automatics. I've got a 5-speed, so I'm not sure if I have to adapt the old one or if I can make the HO TPS send a signal to the PCM.
8) Reuse the Renix distributor and remove the HO ignition coil. You'll have to use the Renix ignition coil.
Hopefully I'll have it up and running sometime this week, after which I'm sure I could give you some better info. Good luck with the swap.