Just wondering what happens if you put the springs on the wrong side of the car. Now they look identical, but they have a 'l/h' 'r/h' designation, which has conveniently rubbed off. After putting the springs back in the car now feels slightly odd, seems to roll more at the back, and is maybe a bit softer at the bacl. I thought maybe the springs are on the wrong side, but i have no idea if that even does anything. The springs in question are King Lows which are progressive. Would this cause said symptos?

To my knowledge no. The original FORD ones are the same for L/H and R/H.

Actually, I have fitted genuine Ford springs...and after market springs.
The Ford ones were identified by a WHITE paint stripe, next to the colour stripe. The white one was fitted to the right hand side.....remember...white is right.
Don't know if they still do that.
Decent aftermarket springs had a sticker on them saying LH or RH.

yeah i've seen pedders and kings with the tags on them. I asked king they said the drivers side spring was slightly higher to compensate for the driver, so if they're on the wrong side the ride height will be off.