Just by going to radials will drop the height of the trailer. Not by 4" maybe 2.
The axle is one piece with springs (Rubber rods) on the inside. No changing the axle unless you no longer want to tow it.
I do not believe 14" wheels and tires will work at all. The capacity is light unless you bought some expensive high load tires. I had some 14" load range "E" tires on a van at one time. It was difficult finding replacements. There is the issue of clearing the drums and bolt pattern to the axle.
1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!