Steve had headers, which I believe are currently up for sale. Headers vs. wet manifolds makes plumbing different.
Do you already have the PCM manifolds and risers?
STEAM LINES
The steam lines need their own separate line directly overboard to minimize backpressure. This is to prevent steam pockets from forming in the block and heads. If you tee the steam lines into another line, flow could stall, forming localized hot spots. The engine will be installed angling up towards the front, I would connect the steam lines to the line overboard at the front of the engine, to take advantage of gravity bleeding air out of the system.
BLOCK HOLES
The front engine plates of the LS rail kits we make are tapped with pipe thread for water in and out of the block. There are several options for connecting your cooling lines to the block. Whichever method you choose, the routing will be the same. The lower rectangular shaped holes, on the timing cover surface of the block, are water in to the engine. The upper round holes are water out of the engine.
PLUMBING THE SYSTEM
There are two ways to plumb your manifolds - 1) Pre-heating the water to build temperature in the engine. 2) Conventional Engine => Exhaust => Overboard.
1) Plumbing for Pre-heating
First, you will need to block flow from the manifolds to the risers. I understand that that there are plates available for just such an application. If the flow between the manifold and riser is allowed to short circuit, water will bypass the engine entirely.
I could not find pictures of PCM LS manifolds, so I am not sure about the configuration of the connections on them. Regardless, you will want to connect the lines in such a manner that flow is either back-to-front or top-to-bottom, to help facilitate bleeding air from the system. Tee or wye the line from the jet pump into into the manifolds. A hose size of 1/2" inside diameter or -8 should be more than adequate.
Connect lines from the out port of each manifold to the corresponding side of the block, into the lower rectangular shaped holes at the front of the block.
Connect lines from the upper round holes on the front of the engine to the risers. I think 1/2" (-8) is adequate, but you could use 5/8" (-10) to reduce restriction.
2) Conventional Plumbing
In the conventional strategy, the water enters the engine first. Tee or wye the line coming from the jet pump and connect to the lower rectangular shaped holes at the front of the engine block with 1/2" (-8) hose.
Make a connection between the upper round holes at the front of the block to the inlet ports on the manifolds with 1/2" (-8) hose.
Depending on the design of your manifolds and risers, flow could either be internal or via an external connection between the manifold and riser. Make whatever connections are necessary.
