Are the floor boards secured tightly to the floor and is there any welting along the edges of the boards?
As for the foaming, there will always be some but it should not be excessive, could be there was water or some other contaminate in there that has not fully been removed yet.
Back in the day people would use any number of things to flush the ******...gas, kerosene, diesel, alcohol or Grandpa's coffee among some.
Could always flush it out real good and start from scratch...I would advise against using Grampa's coffee as it tends to eat the gears.
Give Model A Medic a call in Kansas. He took time explained to me that all of the vendors have their own version of the original 600 wt. I my case the lube I bought was to thin and not sticky, couldn't shift without grinding in all gears. I used his brand and all is ok. No foaming either. Nice guy too.
...I then drained it well and put in Lucas Oil Stabilizer. What a difference! Silky smooth shifting and silent. It's still in there years later, still smooth and quiet.
In 1932, Ford for the first time issued a specification for lubricants using SAE viscosities. Note the gear oil lubricants. Nowhere is 600W mentioned for gear lubrication. I think 600W that was added to the transmission and rear axle by dishonest car dealers to quiet noisy gears.
It has been pointed out many times that the 600W designation had nothing to do with viscosity index or "weight". It was an older term for steam cylinder oil commonly used during the age of steam power. Ford apparently used the term
600W as a part number and later recognized it as SAE 250 in the 1932 bulletin.
There were already millions of Model A Fords on the road when the SAE viscosity index was introduced in 1929. It used Pennsylvania crude as the benchmark for comparison with other base oils such as West Texas crude, with tests performed at 40 degrees Centigrade.