Poston 350 header installation tips:
350 Buick headers can be installed without raising the engine off the mounts, in fact , on ac equipped cars, raising the engine on the passenger side will cause interference with the firewall a/c box.
This job is much easier with the use of a car lift, if you don't have a lift, you would have to get the car way off the ground because you have to angle the headers at a very steep angle to get them to go in from underneath.
Disconnect the battery and remove the starter. On both headers, the lower center bolt between the 2 center exhaust ports needs to be notched out so it is just a slot, I did this with a cut-off tool, a hack saw would work too. Also slot the 2 lower end holes and the center hole on the header gaskets.( this way the gaskets will slip in from the top with the headers hanging loosely in place.) On the driver's side header, cut the flange between #5 and #7 ports. With this out of the way, you can leave the dipstick tube installed in the block, trying to reinstall the dipstick tube with the headers with the flange in place can be very trying on your patience.
Losely install the lower center header bolt on each side of the engine,
make sure it is out just far enough for the header ( now slotted center
lower bolt hole) to slip over the bolt. This will hold the headers in place
while you loosely install the front and rear lower bolts from underneath
the car. With this step done, you can lower the car and slip the header
gaskets in from the top, the 3 slotted holes in the gasket allows them to
just slide in.
If the car is a/c equipped, removing the compressor and moving it out of the way will simplify getting to the passenger side bolts. Now install the 4 upper bolts on each side from the top side and tighten them. Now raise the car back up and tighten the 3 lower bolts ( on each side) from the bottom side, the center bolt on the passenger side is very easy to access from the bottom with the starter removed, the driver's side is a little harder to get to, but it can be done.
If the car is an automatic, you will find that the cooler lines are
very close to the headers, you can either wrap the tubes in a heat sheathing,
or reroute the tubes from going over the top of the passenger side mount
to going under the mount. This will require splicing the lines to get more
length because they will no longer reach the radiator, if you are using
the radiator cooler and factory lines.
With the headers modified as outlined in advance, the installation can be done easily in under an hour, this does not include the time to remove the stock manifolds, exhaust, or any accessories.
Without these modifications, you will spend possibly several hours as you curse those darn center bolts, fight with the dipstick tube reinstallation and trying to get to the dipstick retaining bolt after the headers are in.
This install was done on a 72 gs 350 convertible.