Normal ISO for me for Tri-x would be 250, so, for me, this is 2 stops over exposed. I would hold back development 20% - 30% to protect the highlights (more if contrasty subject, less if flat). The negs will be flat, but you can contrast up in printing. You'll have wonderful shadow detail.
If this puts your time too short for control, then the higher dilution might be necessary. You don't say what your normal dilution and time is, but if you post it, someone might be able to help you figure a dilution change equivalent to what I suggested above in time.