Reverse issues on 904 transmission

RedFish said
The torque converter drains back while sitting. Then the front pump doesn't run in park. Soooo, I start my 67 in park, let it run a minute then switch off, shift to neutral and start again. Torque convertor fills while engine warms. This is how I avoid that short delay followed by harsh reverse engage. I will ad this the drain back isn't nearly so bad if I drive the car consecutive days. I suppose some do drain back faster than others.
I don't know the internal workings of a trans or what part prevents/allows torque convertor drain. If I had to guess... One of those little balls in the valve body not seating just right. So long as I know how to make it function for me, I don't worry about.

Yes, the pump does run in park. It has to. The torque converter hub(or snout) is engaged to the inner pump gear, and the converter is connected to the engine. So, if the engine is running: the pump has to turn.
A trick I learned about torqueflites is this: Start it in park, but instead of putting in reverse immediately, put it in drive first. This will get the oil flowing throughout the trans. Wait a few seconds, then put into reverse. It worked for me in the past and with a harsh engagement in reverse, you'll bust the lugs on the reverse band eventually. Give it a try, you've got nothing to lose.
I got this tip from a transmission builder who worked in the cold part of the country.