You have to buy a new mast to get in-mast furling, the slab reefing mast cannot be converted as it doesn't have the right profile or slot to fit a sail inside it. A new mast is however extremely expensive, not to mention all the other bits you'll need.
There are or were some aftermarket kits that bolt a section to the mast, getting you on-mast furling, but on-mast furling is rightfully seen as rubbish.
In-boom furling doesn't really scale down to 36 ft.
If you really want to switch, it typically makes more sense to sell the boat and buy one with in-mast furling. Unless perhaps you can find someone in a nearby harbour that would like to swap the other way on the same model boat - then you can swap the entire rig and just have to sort out the turning blocks, rope clutches and other minor bits.