Managed to get it working.
Had to use 4 byte float swapped
Next item is for me to take in these integers such as in second example and have them be shown and recorded as what they represent.
This doc might be useful to you: http://wiki.infiniteautomation.com/doku.php?id=tipsandtricks:bestpractice
In my experience (having added probably a dozen different types of device to Mango using Modbus) there is always a bit of fluffing around initially to discover the magic transformation to get from the manufacturer's address to the address that Mango expects.
The first thing I usually do is look in the documentation for the modbus registers and find a register that can be easily identified - usually something like a 'hardware model number' or other known value.
Then you can use the 'Modbus Read Data' and 'Point Locator Test' functions on the Data Source page to test out different registers to try to hit the value you want.
In an extreme example, the manufacturer's documentation may say that a holding register is located at 43004, but you might find that the actual register you need to input into Mango is 3003 (43004 - 40001). Software such as 'Modbus poll' or 'CAS Modbus Scanner' also helps in figuring this out.