TriX has been tweeked since the late 80's but even so you wont get the antiseptic grainless look that converted digi files deliver.
You could try dialing in your development times for that 90 if you feel its a bit low contrast but the nice thing about those earlier lenses is they can give better shadows sometimes.
RB lenses are so cheap you could pick up a more modern lens for not too much I'm sure. I bet you have something your not even using you could sell if you really feel you need a punchier lens.
Those 6x7 negs are worth getting no matter how you do it and I've never really been disappointed with any mamiya glass I've had in a few formats.