1993 2900 Open, 350 Crusaders Maintenance & Replacement ??

[29opensoon]

Trying to go into the purchase with my eyes & ears WIDE OPEN. The boat and engines are 30yrs old. Used in brackish water. Not much for maintenance records. 800hrs, 1 owner. 
What should I plan on Replacing now? 
Yes, a Survey & hopefully a Crusader mechanic will check the Tiara out.

Risers ? $
Elbows ? $
Manifolds  $?
Heat Exchangers $?
Ect........$$ ?

Thanks,