Topping up Series 3 gearbox oil

Hi,
I've got a series 3 1983 that I'm looking to top up the gearbox oil levels.
I'm looking to top up the gearbox, transfer box & fairley o/d levels.
Can you advise how I do this.
I know there are level plugs to the side but I take it you top up from the top?
I've lifted the floor (for something else) and wanted to do this while I'm here. There seems to be 3 plugs to the top, one for each unit, are these where you top up?

Thanks.

Not sure about the overdrive but I've found the main box and transfer boxes are usually easier to fill from the top but you have to pinch the oil bottle tube when you're full or oil goes everywhere. The filler plugs are on the side of the boxes about half way up.
The filler plugs are 1/2" square and there's a 1/2" socket that fits the square end of a ratchet driver (13 14mm 12 point? can't remember) so the square hole on the socket can fit the filler plug (fits better than the 12 point does especially if the plug's a bit rounded).

oxides said:

The filler plugs are on the side of the boxes about half way up.

Click to expand...

Are these easy to fill half way up and on the side?
What's the best way, is it just a funnel and take your time?

EP oil bottles usually have a collapsible or additional tube to get the oil into a small hole. If you buy 5l bottles keep some small bottles handy to decant into. Failing that you can get funnels with flexible spouts or large syringe like pumps with flexible pipes.

oxides said:

EP oil bottles usually have a collapsible or additional tube to get the oil into a small hole. If you buy 5l bottles keep some small bottles handy to decant into. Failing that you can get funnels with flexible spouts or large syringe like pumps with flexible pipes.

Click to expand...

Magic thanks!

Sealey Oil Syringe I find the easiest way.