As far as I know T1 Race Development side feed to top feed conversion rails fit preFL injector risers, aka the cast alloy pieces that would house TGV’s on post FL and G3 wrx etc.
So if you found those online and looked at the compatibility options you’d have your answer.
Here they are:
https://www.t1racedevelopment.com/produ ... 04-06-sti/So then you might lookup USDM STi injector riser part number, see if it’s interchangeable with those found on the ej20y/x…
Well maybe, USDM did have TGV’s in 04 at least.
Anyhow I do have a set of T1 rails installed on a preFL intake manifold on the bench plus a spare set I got along the way.
The top feed injector bases are much narrower than side feeds, your options are specific-seat injectors from ID as per the product link above, Radium injector seat adapters or just try going in to see if the standard seats will seal.