I have a 60 f100 that was an old farm truck. It has heavy duty suspension and rides like a tank. I'm wanting to lower it by removing some leaf springs. How many can I safely remove?

 

Here is something that appeared in a previous post regarding rear springs...

Recommendations in the Mid-Fifty catalog. "Starting with the shortest, keep #1, remove #2, keep #3, remove #4, keep #5, remove #6, keep #7 but cut off the wrap 1 1/2" from the eye. " With reversed eye springs this is supposed to drop the rear 3 to 3 1/2".

Assuming that you followed the above or something similar, it would depend on what you want and how the truck feels now.
If the ride is already soft, I would remove the short one to drop it a little more but maintain as many long springs as possible.
If the ride is still too firm, I would look at removing one of the longer ones as this will tend to soften the ride. I would not remove the spring immediately under the main spring (#7 above).
Recommendations in the Mid-Fifty catalog. "Starting with the shortest, keep #1, remove #2, keep #3, remove #4, keep #5, remove #6, keep #7 but cut off the wrap 1 1/2" from the eye. " With reversed eye springs this is supposed to drop the rear 3 to 3 1/2".

Assuming that you followed the above or something similar, it would depend on what you want and how the truck feels now.
If the ride is already soft, I would remove the short one to drop it a little more but maintain as many long springs as possible.
If the ride is still too firm, I would look at removing one of the longer ones as this will tend to soften the ride. I would not remove the spring immediately under the main spring (#7 above).