are headers the same on la and magnum

The TTI headers "fit" both Magnum and LA heads. The bolt pattern between the two are identical. But the shape of the exhaust ports between the two heads are slightly different and TTI headers tend to favor the Magnum heads. On my LA Edelbrock heads the headers hang into one side of the lower port corner on the four outer most exhaust ports of the engine. I had a header fabricator take a look and he didn't think it was that big a deal given roof of port is where most of the flow occurs. But given the price of TTIs one would think they would sell an LA and a different Magnum header so no compromise would exist. The sealing surface where headers hang into the port if thin requiring good header gaskets. I had the header fabricator add a weld bead to the header flange to get more sealing surface. I run FelPro Performance header gaskets no leak issues at at all. I might be losing 5 hp or something like that who knows due to header hanging into 4 of the ports.

Over the years I've done a couple of magnum head to LA block conversions.
Thru the years they made a few different gasket configuration for the LAs. Think of the years where LAs had the injector holes for the AIR pump. I believe I ended up using gaskets for an older LA before that started. I remember one combo where the manifold port overhung the head port and I had a helluva exhaust leak. Think that was maybe my 83 truck. I ended up putting a set of hooker super comp headers on those magnum heads, header application was an older truck (70s if I remember correctly) and no issues with port match. At least none that caused a leak, I never did get into it to a point of doing a gasket match as you would when porting or anything like that

They are correct. I have used TTI headers (same ones) on both an LA and Magnum head engine. I really like Remflex gaskets.

yup, I reused my hedman headers on my old 5th ave when I switched from an LA360 to a magnum headed roller 318.....