same thing? which ones better? how much hp increase if any?

 

oops.

 

I had ran a TB mounted K&N on my car when I first started modifying it. Later on I made my own custom air intake with 3.5" tubing, impala ss elbow and the same K&N. It's been a while but I remember picking up a tenth or so at the track. This was all done when I was running a 305. All the TB mounted filter will do is suck the hot air from below. Remember this will only work on the 90-92 Speed Density systems.

Here is a link to what I built: http://www.i-55.com/~davidlt/air_intake.htm

 

I used the TB mounted K&N for a while. Last summer I switched back to the stock air filter setup and didn't notice a change other than the sound. I think it might even hurt performance because of the air temp. Your best bet would probably be a couple of stock replacement K&N filters and reduce the restriction under them. But even that would not make much of a performance difference on a stock 305.