I thought that was the oil cooler? I think on my 420's they are on the starboard side of the block, but I could be wrong.

I've got to say the obvious. The cooler is the one the cooler lines from transmission go to..................Probably tucked under one side of motor ,under the mounts

Would a Dexron fluid work in a velvet drive trans??

Crazy if it is being blown out the cooler on the pressure side and being dumped out on the cooling water side being it is a fresh water boat. But killed a trans in saltwater having the same thing happen with the cooler going out in minutes. /

It was not a cast cooler that went out. What is your cooler?

yes it will work. A buddy of mine runs it in his. I've always used type F based on the merc manuals and Marc from Bam. I see no reason to steer away from what has worked for many years and many velvet drives behind some big power.

Huber and Speedmasters always said F only. Everything else increases your chance of slip and failure. It's cheap insurance