Probably gonna be -6an fittings. Here's a chart on how to measure and get the correct sizes for both -an and NPT.
This link goes more in depth on how to correctly measure for NPT fittings. http://www.plumbingstore.com/pipethreadsizing.html
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1987 IROC-Z 305/5 speed
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-305 block .040" (312 cid), Speed Pro hypereutectic pistons, stock rods; shot peened/polished with arp rod bolts
-Hedman shorties and Y pipe
-Hooker 3" Catback minus cat
-Edelbrock Vic Jr converted to MPFI; gasket matched, mild port and polish
-Holley 750cfm throttle body (modified)
-26lb/hr delphi fuel injectors
-Comp Cams Hyd. Roller cam 262hr-12
-Holley Annihilator CD ignition
-Holley LaserShot Pro coil
-Summit 8mm spiral pro wires
-Fluidamper 7" balancer
-Cast aluminum timing cover
-March Billet underdrive pulleys
-7730 ECM conversion and DIY PROM burning using TunerProRT and PPII
-World Products SR Torquer heads, full port and polish, Manley stainless 1.94/1.50 valves, high flow valve job
-GM 3.23 gears
-T5 swap
-Centerforce dual friction clutch
-VDO and autogage instruments in custom acrylic gauge panel
-Minor weight reduction including: A/C removed, smog removed, front sway bar removed, undercoating removed, stereo removed, most carpet padding removed, and wonder bar removed.
-255gph walbro in-tank fuel pump
-edelbrock fuel rails
PARTING OUT, CHECK OUT MY THREADS ON THE CLASSIFIEDS BOARD | 
