Replacing head gaskets

Victor Reinz/Ishino/Stone are all OEM equivalent head gaskets. I got the set of VR I used off of Rock Auto. We compared them to a set of original Nissans and other than a little Nissan logo on them, we could find no physical differences.

For the studs, go with a set of Dorman replacements rather than the stainless.

Fel-Pro is good for anything outside of the head gaskets. All the other gaskets on my engine are Fel-Pro.

As far as doing it in the car, I have nothing for you there, I've always done it with the engine out of the car.

I did it with engine in the car. It's only annoying if you leave the turbo and exhaust manifolds in there too.

I have done in car hg replacements twice now. Very straight forward and not difficult in my opinion. Just make sure you clean the mating surfaces very well and id suggest having the heads cleaned and checked at a machine shop, as they can clean them better than you ever could with basic tools. I leave the turbo side exhaust manifold on but remove the passenger side. I also skipped the step where you loosen the head bolts before the final torque sequence. I think the rocker shaft loosening, and tightening, mating surface cleaning, and lubing and tightening of the head bolts are the only parts you need to really be careful with.

Any advice on cleaning the mating surfaces, and what would I expect to pay for a shop to do the heads?

NA here, so does that make a difference? Seems easier to take the exhaust header with the heads, especially since I have a leak on the driver's side.

Depends on the shops preferred method of cleaning and on how extensive you have them run checks determines the price. They can mill them or tank them. And having them check for head flatness and warpage as well as a vacuum test to make sure there are no internal cracks. I have my shop do both since to do the vacuum test it has to be tanked according to them. The cam does need to be removed for that if they do it this way. That being said our heads really aren't that prone to cracking so I'm sure some would view it as unnecessarily cautious. I think it's better to err on the side of caution so I don't have to do anything more than once. So the bill (depending on which way you go) should be about $100-$170 depending on where you live and which route you go. Mine was $200 but I had them weld some electrolysis up as well.

As far as cleaning the block side it's easy. Iron blocks like ours can be scraped with a putty knife or any iron/steel scraping tool until it's as clean, and smooth as possible. Be sure not to drop gasket material in the galleries in the block. I had a vacuum in one hand, sucking up crap and scraped with the other. Then go over it with a rag and acetone to remove any oil and other residue. The heads being aluminum are much softer so metal scraping tools and wire/nylon wheels can remove metal from the mating surface or mar it so only plastic scraping tools can be used which are useless, hence why I think a machine shop is the best way to get the job done.

The reason why I leave the manifold on is I'd have drop the turbo to get the manifold off the exhaust studs on the head since there is not much room until the turbo hits the frame rail. I don't think an N/A would have that issue. I think you should be able to get your exhaust to flex enough to take the manifold off in bay. If you do leave it on just pay attention to the dipstick tube as you pull the head/manifold out. If it's a cracked manifold leaking not just the gasket it should come out anyway, might as well leave it attached and remove both.

As mentioned already, the most important part of this process is having a reoutable machine shop resurface the heads. I've been through multiple HG jobs on Z31s and skipping this will only result in having to replace it again in the near future.