2000 Boxster S exhaust manifolds

[Blue-S]

My 2000 Boxster S 6-speed has at least one crack in the exhaust manifolds. With the car on a hoist, I can see a crack in the header pipe just inside the flange where it bolts to the head at cylinder #6. The symptom is a tick sound (like a cracked header) which is very noticeable on cold start, but becomes less audible as the engine warms up. I have identified three inexpensive repair options:

1. remove exhaust manifold/cat assemblies and repair the cracked areas by welding, then reinstall

2. buy cheap headers on ebay, then install and relocate the downstream O2 sensors after the main catalysts, preventing the car from failing the cat efficiency monitor

3. buy used 1997-99 2.5L stock exhaust manifolds and cat/pipe assemblies. Relocate the downstream O2 sensors to the 1997-99 post-cat locations. This approach has the advantage of appearing stock to a California smog inspector, as long as the individual does not know their Boxsters really well. Will the 2.5L manifolds match the 3.2L ports? I don't know.

I am new to Boxsters, but I have been ASE Master and L1 Advanced Engine Performance certifed since 1998, so I don't anticipate any major problems doing the work myself.

Which option has the best chance for success?