I don't know, but my instincts say "No". The '89 Montero ECU has a very conservative ignition timing curve.... and the curve is based on the valve timing of the Montero heads. A change in valve timing can require a change in ignition timing to make maximum power, but I suppose if the difference isn't too great, ignition timing might not be a huge issue relative to valve timing and the '89 Montero ECU ignition curve MIGHT allow you to run 10:1 CR on regular grade gas without damage, but it's a guess at best.

The injectors appear to be the same flow rating. The Montero injector is a B210H and the Diamante is an N210H - both are 210cc/min but there are 2 questions:

1) The injectors may have different impedance values which would not work unless the correct injector was paired with the ECU.... not a big deal as long as you're aware of it when replacement time comes.... the Nippon-Denso manufacturer's number is cast into the injector, but in the case of the Montero's B210H, the Denso number is actually INP-051. The Montero injectors are high impedance.... don't know whether the Diamante injectors are high or low impedance and I've looked in several reference places, but can't find anything on them. I did see in another reference that there are 2 injectors used in the SOHC Diamante engines: '92-'93 uses MD156760, '94-'96 uses MD189023..... neither are the same as the '89 Montero's MD111421. If you want to solve that riddle, you can pull an injector electrical connector and measure resistance across the 2 terminals..... high = 10-16 ohms, low = 1.7-3.0 ohms.

2) Even if the injectors have the same impedance, the two computers may have a different pulse width programmed into the processor for similar load and rpm metrics - particularly since the HP is different..... more HP at a given rpm and load requires more fuel, so for the same size injector, the pulse width needs to be longer in order to feed the HP need. Could the o2 sensor trim enough to make up the difference???? Dunno.

I don't think you can figure out anything by looking at the cams unless you put them on a degree wheel.

Why don't you remove the ECU from under the passenger side dash and see what number is on the ECU case? That might tell you a lot.

If Charlie is reading this, maybe he'll chime in - he knows the Mitsu engine variants pretty well.

Frank