On my 1974 144, I custom make the system at our local muffler shop.

Piping wise, the 74 is closer to the 240, as the gas tank was moved closer to the rear seat for rear end collision safety reasons. Therefore, the routing of the pipes at the rear is different from the pre 74 models.

Both original mufflers on my 74 is similar to the earlier 144s, but is smaller than the 240s. What my local shop does is to use pipes for 240s, and weld in the 144 mufflers. Works very well, and its been over 5 years since I did any work to the exhaust system.

Also, the gasket between the exhaust manifold and the dual downpipes is the same between my 74 144 and my 1996 940...

Hope this helps.
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...and the bricks keep on rolling