I need to know the following: fuel tank size( tank capacity),radiator capacity, oil capacity and oil pressure range for a 1987 Nissan Maxima

This information should be found in your owner's manual . Go to the index , and look up " Capacities " , or " specifications " . There will be two engine oil capacities , with and without changing the oil filter . ( Changing the filter adds 1/2 , 1 , 2 , or more quarts of oil that is needed for an oil change . )
you should have the owner's manual , if not they are available form the manufacturer , from the conversion manufacturer , the dealer , on line , from " junk yards " , and often your local librarian can help you .
You can find out capacities from the following web site ;

http://www.autozone.com

( You might want to click log in , and fill out the create an account , so you can have all this info whenever you want it . )
At the bottom of the page , click on " Site Map " . On the site map page , find repair help , then click on " Vehicle specifications " . Fill out the year ( 1987 ) , make ( Nissan ) , model ( Maxima ) , and engine ( ? ) , click add vehicle , and it should give you the information you want .

One last thing . there are several aftermarket manuals , such as Haynes , Chiltons , etc., ( often available at your library ) .

Fuel tank, 17.2 gallons. Radiator capacity, 1.25 gallons. Oil capacity 4.5 quarts with the filter. Oil pressure, 20-50 psi.