The 87 through 95 is 350 is the LO5 Throttle Body Injection, Swirl Port headed engine. It uses a one piece rear seal which drives a different, smaller diameter bolt pattern on the crank flange and requires a small amount of external counter weight on the flywheel or flex plate, so these parts are unique to these and the L31 Vortec engine of 1996 through 2002.
At the front end there is a serpentine belt drive for the accessories. This changes the type of pulley to a wide ribbed type instead of the narrow V groove type. The coolant pump and mechanical fan on these engines is a reverse direction drive from that of earlier the V-belt engines. These engines can be refitted to V-belt drive using the pre-1987 long pump and fan. All the other accessories turn the same direction whether serpentine or V-belt and pulley types will interchange on their shafts.
The Swirl Port heads appear to have the same bolt pattern as the pre-1987 heads but it isn’t quite the same so earlier intakes don’t simply bolt to those heads. The difference is the bolts by the plenum were changed from being 90 degrees to the machined intake surface to 72 degrees to that surface. So the TBI intake does not interchange to the older heads nor do those older carb intakes interchange to Swirl Port heads. This is a problem that can be worked with aftermarket parts if needed. The other thing with these heads is they use a self guiding rocker so there is no machined push rod guide in the head casting. Older heads bolt to the block.
Internal to the block the rods are powder forged net sized so you’ll most likely not see balance pads or balance grinding marks on the rods. The length of cylinder extension into the crank case is reduced as is the overall length of the piston skirt. For the rotating assembly this is an overall weight reduction of the pistons and rods so the crank balance of these engines reflects that.
Most major parts interchange but these are the most common differences. Many of these 87-95 blocks were used for passenger cars and trucks. Most passenger cars got factory roller cams but the same block in a truck most likely got a flat tapped. So almost all truck engines have the cast provisions for a roller cam which will be 3 valley bosses that mount a gadget called the spider, it is used to hold what are called dog bones which keep the roller lifters aligned to the cam. The lifter block pairs will be taller for the longer roller lifter and will be machined across their tops. In the timing case on the front of the block the thrust face for the cam gear will have an ear added to each side that is used to mount the roller cams thrust plate. These features may vary from being rough cast to partially through completely machined and threaded where needed.
The cam timing sets are unique for flat tapped or roller cams. A flat tapped cam fits in the conventional manner and uses the same old flat tapped cam gears and chain. The roller cam puts a plate on the front of the original thrust surface where the flat tapped cam gear would ride against the block. The factory production roller cam has a stepped nose extension of about 1/8 inch that passes through the thrust plate. This uses a unique cam gear that is approximately 1/8 inch less deep on the rear of the mounting hub. The bolt pattern is also different with the mounting bolts in a smaller circle so the old metal retainer does not fit and aside from Lock-Tite no restraint is applied. Also note if you get switching cams around that most factory roller cams do not have a mechanical fuel pump drive and many 87-2002 blocks do not have a finished pump mount this through 95 is inconsistent and is gone from 96 upwards as from 97 on these engines are fuel injected in some form or another. Industrial and marine blocks still have finished fuel pump pads and their cams have pump lobes.
Yeah it’s a lot of changes. The one piece rear seal block can be converted to a two piece seal with the older style crank and with a 1 to 2 piece seal adapter, but not the other way for a pre-1986 blocks. 86 was the rear seal, crank, rods, pistons, and fly/flex year. 87 did the top end.
Good luck, bring questions before you spend money. Bogie
