whats up with the 2.45 8 1/4 housing?

What gear ratio does your car have now? No way any of us can know, only you. Maybe your misunderstanding what it's saying, in that case it means what your looking at won't work if your rear end has 2.45 gears, not a reference to a housing ID #. The 2.45 geared rear end was an oddball that higher numerical factory gear sets or sure grip units won't work in. If I'm not mistaken they have overcame that problem with aftermarket parts. Cass at Dr.Diff would be the man to talk to. I'm sure he can tell you for sure what will work and what won't.