I want to put a 2010 Street Glide 2 into 1 exhaust on my 2008 Classic.
Will the factory 02 sensors in the 2010 pipes work or will I need to use the 08 sensors?

 

I'm pretty sure you need an 09 pipe since they have 18mm bungs like your 08. You will also need to change your oil pan to fit the new style crossover pipe.
Read your question again the newer 02 sensors are 4 wire heated and your 08 sensors are 2 wire

 

The 2010 pipe uses 12mm 02 bungs. I don't remember if the 2008 is 12mm or 18mm, but the position is different. If you have a tuner that doesn't need 02 sensors you just plug 'em. I put the 2010 pipe on my '07 Road Glide. I have a ThunderMax & need the 18mm bungs, so I had a couple welded in the appropriate positions. Didn't cost much, but be VERY careful about marking the location first. There's not any extra room.

BTW, the only thing extra you will need is the transmission mounted bracket to hang 'em on. It's the same as the one you have except that it's about a half inch longer & costs a dollar or two. Pick one up when you get the new exhaust gaskets.

 

I have to 02 sensors that came with the 2010 St. Glide exhaust, they are four wire.
Looks like I'll have to weld in new bungs and use the original 08 02 sensors.

 

Can't tell you for sure, but I believe both are narrow band sensors. I'd compare the plugs on the sensors. Count the pins, & note the pin location, if they're the same I'd plug 'em in & try 'em. They're not likely go fry anything, but you might get some error codes. Easy enough to reset......