I'm thinking of getting the ebay tmic, I'm wondering if my Perrin y pipe would work with a larger tm? I noticed some of the bigger ones include a cast y pipe and silicone elbow.

Could I reuse the oem piping and perrin y pipe with one of these intercoolers?

 

How about a link to which ones you are talking about? You might want to send a email to the vendor themselves so you can get actual dimensions.

 

I would recommend saving your money and sticking with the stock TMIC or getting a different aftermarket TMIC when funds allow it. The ebay TMIC fitment is poor at best. I've seen more than one local Subaru mechanic struggle with trying to get that abortion to work.