So...I have a 90 miata w/ ~140k miles on it w/ the greddy turbo for about the last 25k. My miata is an early 90's one and has the cute little pos short nose crank which i have observed in all its wobbly goodness. So I am planning on (and slightly hoping for) an engine failure so I can upgrade. I was wondering what mods i can do that will transfer to a 1.8l yet still work on the 1.6 till i blow it up. Fuel pump, injectors, afpr,...etc.

 

Pretty much everything. If you plan on keeping the turbo you'll have to use an HKS manifold and rework the downpipe a little. But other than the engine being a little larger, there isn't much difference that I can thing of.

 

get a capri 1.6/ gtx motor or start building a new longblock to minimize downtime.

 

Cheesecow, I'm assuming you know that a 1.8 is (almost) a direct swap for a 1.6. The things you need for the swap can be bought in kit form from
Flying Miata: http://www.flyinmiata.com/index.php?dept=67

If you already knew that, then just like Braineak said.

Used 1.8's are for sale in the m.net classifieds all the time. There are guys with 150k miles on FM2 kits running 12psi. Unless you're planning on more boost, a stock motor is plenty strong. I know you're emanaged and intercooled (the pure sex over-the-top route, I plan on following your exact setup for mine)... so the next step might be WB02 for tuning... maybe bigger exhaust... maybe set aside a fund for a 1.8 clutch/flywheel combo... maybe 1.8+Torsen driveline upgrade... maybe Link...

You should probably pick up a few ponies by going to a 1.8. I think your overall best move would be a 1.8Torsen rear. You can usually find a full setup, driveshaft/axles/carrier/dif package for around $800. Your current clutch/flywheel (I assume it's not still stock) will swap straight over to the new motor. You'd still have to use a 1.6 Link if you went full stand-alone.
Hope this sparks a thought...