the same day i put the motor in (to replace the 253 that was in it) i broke 1st gear
i kept driving it now the whole box is full of metal soup and it barely drives

So i need a new box, i believe the box in it is a w58 supra 5 speed, I was going to put an r154 in it but i just rang a guy to do it and he told me that it wont fit, will need a new bellhousing etc. is there a stronger box i can bolt up? or do i need to go custom shit?
the motor has a forged bottom end high comp pistons, a mild cam and headwork, i'm led to believe about 300ish hp.
If you can offer any advice i would love to hear it
Matt