how much of this kit can I use on my 1.6l if I got it
 

Fm miata full turbo kit with hydra 2.5 from a 99 miata to a 90 1.6l
I know the hydra is out and the manifold
how much of this kit can I use on my 1.6l if I got it
thanks for the help

As you said, everything but the manifold and hydra. You'll struggle to get paid anything for the 2.5, and depending on the condition of the manifold, you may get a couple hundred bucks for it from a 1.8 owner, or hold on to it until you upgrade to a 1.8.

Most likely the downpipe won't fit, at the very least you'll have to make a custom exhaust connection from the end of it to your current exhaust.