cat swap question

["dms" <dms@domain.elided>]

hi all.

my cat converter is shot & needs to be replaced, however,
the $380-450 price tag is sticker shocking me, so, since i
can do a tad bit of welding i was thinking i'd buy a cat for
another car & weld it in place. has anyone done this before?
and if so, what make/model car's converter should i buy?
is there an oxygen sensor, and if so, is it a generic sort of
hole that it threads into, or alfa specific? the car is an
86 spider grad.

thanks much!

dave sisson
houston, tx

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