I used D76 for years (not the same batch) in deep tanks with floating lids. The slot processor would just be a smaller volume than the five litre tanks in the lab. There was a replenisher used in those days and with a high volume of film the tanks got refilled only a couple of times a year, but replacing a small amount of dev every few sheets would work reasonably well as an imprecise alternative to lengthening the dev time. Remember that four sheets of 4x5 is the same-ish area as a 135 or 120 roll, for time adjustments. An alternative would be using a slosher in trays, but there is more setup and breakdown time involved then.