Jessie,

Go to Google.com and look for an article published by HotRod magazine
pertaining to installing a Corovette LS-1 engine in a Z-32
1990 thru 96 300Zx.

You might be able to get the article from HotRod
mag, if the have archives on their website. Also, I think Stillen.com
sells the conversion kit for motor mounts, not sure if that's the right
website. But using "Nissan 300Zx with Chevy engine" search terms on Google
might bring up the article, somebody is bound to have published it to the
web.  

I saw a Z-32 on EBay last fall with an LS-1 mounted in a 2+2 300Zx. 375hp
and the engine is 50 pounds lighter (aluminum block) and there is about 2
inches of clearance on both sides to change spark plugs. No room to work
on factory engine, unless you have little hands or the right tools.  Good
luck.

WB