No an internal mast step works just fine!!!!!
The pic below is at a high resolution so you can zoom in and get a close look.
Don't click on the photo, just increase your zoom level to 1000%.
Hold "Ctrl" and tap your "+" sign then use the side bars to position the bit you want to see. "Ctrl minus" back.
Greg has used this method here for some time now and is very successful.
His is mounted to the LLM chassis with 4 bolts on a square flange. This makes it fully interchangeable with ones of different rake angles. (or simply reversing it for long curved masts)
He used the pulley downhaul system off the base of a windsurfer mast extension and wrapped it in carbon to bond it to the base of the mast, so the downhaul rotates with the mast.
You still need to internally reinforce the mast with at least 600mm to 750mm of aluminium/steel tube that is a snug fit. (48mm OD or if they are the slightly smaller ID masts - 45mmOD. All my 3mm wall aluminium tubes have a curve in them so the thicker the better. Cut the 4x 150mm slots down from the top so these fingers flex and you don't have a stress point where the tube top finishes.).
Greg leaves his internal strengthener tube just pushed up the base of the mast so he can remove/alter it, as is needed.
It actually helps the mast to rotate easier when jibing.
I hasn't got anywhere to collect the grit and grime and if you are using camed sails the lower rotational friction is a real bonus.
He is bringing it back to Lake Lefroy so I'll try and remember to get a better photo of it for you.
I have lots of Gopro vids of it working, but cant sort out how it upload them.
My computer cracks a sad.