Exhaust Laws?
 

i have a 96 f150 and both cats are basically shot, i was wondering if i could replace both with 1 high flow or do i have to do a 1 for 1 swap?

Technically, you have to do an exact swap to comply with the law, which states you must retain all factory emissions equipment in operating condition.

Normally I'd just say shove on a big cat and call it a day, however you have a 96 truck, which is ODB-II compliant, which allows (under new law, and new inspection station equipment) to hook into your ODB-II connector, and monitor your truck's computer information regarding operation and emissions. You may, or may not pass if you just put one cat in, it depends on a lot of variables, unfortunately.

i guess ill just play it safe and put 2 on there... or maybe ill just put 1 high flow on...i got 2 years till inspection anyone, just keep the ones i got on it now, i guess my question now is where do i get a small y pipe to merge the 2 header pipes into 1

I have another year plus, myself. Which is why when the cat died, I just hollowed it out temporarily. I'll be putting on a new exhaust system anyway, when I put the stroker in. Didn't want to buy two exhaust systems within year.

Headers... okay... um... if the the outlets are the same distance apart as stock, you can use the stock pipes and either flange or flare the ends, depending what kind of fittings/brackets you have with your headers. Or, you can make one out of exhaust tubing. Not too difficult. Any competent muffler shop can make one if that's out of your handiness.