Chuck:
http://www.rceng.com/
p/n: SL4-205
Make sure to tell them what year of ZR1 they are for.
No mods necessary, just stick them in.
You will need plenum gaskets.
Contact Jeff Flint on this forum (JEFFVETTE), he'll set you up.
While you're in under the plenum be sure to check all the vacuum & sensor hoses and connections. Replace any that have gone soft or cracked.
Make sure to retorque the oil breather box bolts and the injector housing bolts too. They tend to loosen over time.
Good luck!
Let us know how it goes.
Regards,
TomC
'90ZR1 #792