Big Block Oil Passage Mods
here is work that should be done any time you do a full rebuild on a 400 / 430 / 455 or if you are having oil pressure issues:
Jim Weise's block mods
http://www.trishieldperf.com/455_block_mods.htm
Timing Cover
http://www.buickperformance.com/OilingMods.htm
Block Passages
http://www.buickperformance.com/oilflow.htm
Optional
Neoprene Main Seals
Front: National Part # 450446 or Federal-Mogul #470543 or National Oil Seals #450446
Rear: Fel-Pro #BS30135 or National Oil Seals #5068
Checking for Oil Pump Wear; a definite must for pressure issues
http://www.buickperformance.com/oilpumpwear.htm
Plumb for a rear mounted Oil Pressure Gauge, much better than the front mounted stock sending unit
http://www.buickperformance.com/Oilmods.htm
Strengthen the Lifter Valley; some are very leery of using Ti putties/epoxies inside their rotating assemblies, use at your own risk
http://www.buickperformance.com/455LV.htm