I'm asuming you are talking about the 87-93 dash. If you are contact Myke86GT...he has it in his 86. I personally prefer the more open feeling of 79-86 interior...but to each his own.
It's not a direct swap, but really isn't a hard one. The biggest problem is wiring the gauges & heater controls if keep the 86 harnesses. You will need to modify the mount points on the body at the top of the dash where it meet by the windshield. Have to bend a few tabs and trim one alittle and use a little longer screws.You will see what I mean when/if you do it. Also you will need to move the e-brake handle over and trim the hole where the cable goes through the trans tunnel for the center console to fit. Also have to add the back mounting bracket for the center console, the one the arm rest bolts to. No biggie there just find the right location and use some self tapping screws.
But back to the wiring, if you are using the 86 hanress you will need either to splice the 86 harness with plugs for a newer harness for the gauge cluster & heater controls. You can run aftermarket gauges, or swap the dash harness. When I did my 86 I re-wired the whole car with 89 harness(front to rear), mainly because my car's harness'es were in bad-bad shape when I got it, and plus I wanted mass air. There are probably some stuff I have forgot, it has been about 2 years since I did the swap.
The dash itself it easy to swap in, just the wiring can be troublesome.
The gauge cluster harness is the dash harness. Only thing is, I'm not sure about is using the 86 engine harness with the 87-89 dash harness. And if you do it that way, you most likely would have to use an 87-89 harness. If you don't have mass air, this would be a good time to do it. That way you could get a dash and engine harness from the same year(89) along with the cluster. The cluster will have to match the dash harness. 87-89 can be interchanged, & 90-93 can be interchange, but can't interchange between the two year groups. Also the engine and dash harness can't be interchaned between the 2 year groups. Plus the 90 engine and dash harness are a group by their self. The 90 harness looks like the 87-89 harness and will plug up to a 87-89 harness but won't work without some mods. The 87-90 have 2 plugs behind the driverside strut tower by the EEC test plug, a black and grey one, and the 90-93's have only one plug red to redish borwn. To tell an 90 harness form an 87-89 is look by the mass air plug, it will have a white plug for the air bag sensor.
Well if any of you 79-86 guys are going to convert your dashes to the 87-93, let me know how much you want for your old dashes. I need a new one my old one is dying! "gotta love the Arizona sun dries up everything even cars"
I'm not to sure about the wiring on an 86 engine working with an 87 harness. I'm guess it could be done if you went wire by wire thought the 87 harness and just picked it apart that way. When I did the swap in my 83 I already had 91 mass air motor in the car so everything just plugged in. I've never been one to cut wiring harnesses apart mostly because I've seen some very bad examples of it and don't care to deal with it again. I've never worked with an 86 engine so I 'm not really sure how it's setup compared to the 87+ as far as sensors etc....