Fiat Spider Exhaust
When this 1979 Fiat Spider was purchased, the catalytic converter had already been removed. The intermediate exhaust pipe appeared to be from an earlier year. This posed no problem for my state inspection, as vehicles 35 years and older are emissions-exempt (North Carolina). Check yours.
Aside from California models, 1979 Spiders have efficient exhaust manifolds and engine pipes, which are referred to as the 4-2-1 style (four into two into one). They were designed to fit a three-bolt catalytic converter.
The 1979 California and 1980 Spiders came with a restrictive 4-into-2 exhaust manifold. Later fuel-injected Spiders (1980-1985) used the 4-2-1 style exhaust, but had a four-bolt catalytic converter.
Exhaust Manifold Oil Leak
The Spider engine has two exhaust studs that are open into the cylinder head where oil lays, between valve springs. These are the studs that are second from the front and second from the rear of the head.
It turned out that a few exhaust manifold studs on my car had been previously replaced with bolts, which was allowing oil to leak on the manifold. This was resolved by finding the correct-length metric studs and installing them with non-hardening sealant. Torque specs are 18 lb/ft.
A glass-pack muffler came on the car when purchased. It looked stupid and sounded worse. I found the same (O.E. style) muffler offered on several different websites, ranging in price from $85 to $235. It's worth your time to shop around before you buy any parts for your project car.
After trial-fitting several times, the rear muffler was replaced. The original brackets were missing, but replacements were easily fabricated.