I'll say that Mcbride19 is right... the SD4 is just a SD3 with a box around it.. nothing else. It still uses the horrid jig-saw extruder. so my advice would be to print either the MK4 or MK5 extruder from lawsy and to take a look at the thread i made about upgrades for SD2/3.
and just think of how much 300$ extra really is, you could buy him a bunch of filament for 300$

Nice gift btw