reverse doesn't work in 904

Yes, check the fluid level in neutral, not park. The torque converter does not fill in the park position.

If you can drive it see if you have first gear braking when the shift lever is in manual low. If you do the rear band is working. If it just freewheels like it's in neutral whan you let off the gas in first gear then the band isn't applying or is way out of adjustment.

You don't need an inch pounds torque wrench to get close, snug up the adjuster lug, back off 4 turns and tighten the lock nut. This is close enough for testing. The major concern is not having the band too tight, not too loose.

If these all fail then the butchers at Ramco (did you know that over half the cars we service don't need a new transmission? But we try to sell you one anyway) have screwed up your valve body.

Good luck on that. You might as well just get another one and start fresh or buy a Turbo Action or other valve body.