Need some help after internet searches turned up nothing of use, at least nothing of certainty.

My boys 2004 WRX engine is about dead, new coils and plugs and still have misfires on 1 & 4. With 225K on it, we decided not to rebuild and just drop in our 207 V5.
I am installing a new timing belt kit with cam/crank seals, injectors,pump, studs and head gaskets this weekend.

Here is my dilemma. I have a T04b Super V trim Garrett t4 split tang p trim turbine housing, 60 a/r compressor housing.
I see pedestals for t3, but not t4. I find (grimmspeed and others) that make a eternal wastegate up pipe for the 02-05 wrx.
However these are for the stock bolt pattern turbos, which of course are not t4 bolt patterns.

Anyone done something like this, is it all custom fabrication ?

Thanks for the input,
"E"