Technical Baron Heads Temperature senders

I run Baron heads on a H&H built 276 Flatty.

The removable water rail seems to taper back where I was planning on drilling for temp senders at the rear.

Holding a regular 3/8" 8-BA temp sender up it seems like it'll be snug fit in the internal Diameter of that rail and coolant might not flow around the temp sender very well. Also the sender would extend past the 3rd water neck inlet making a choke point.

how much clearance I would need around the temp sender to allow for proper coolant flow?

Is there a dual prong Flathead style sender with a smaller NPT diameter anyone can recommend?

I stumbled across this picture showing someone drilled a set for temp senders.


Thanks. I don't want to mis drill on these rails and want to see what others have done.

Here's a photo of my motor I randomly found on the net. You can see the taper at the rear of the rail