Would a set of sails from a modern rig work on an older Hog stepped rig (NSM4 3374) I'm struggling for a decent used set, and new baby means the better half wont let me buy a brand new set

In general terms yes but you'll have to tweak your rig to suit. modern rigs are basically bendier which means sailmakers design the sail in a different manner eg more initial luff round, so you will have to mimick that with your alloy rig. freeze the mast at deck level & induce more prebend via the spreaders (rake them further aft). Basically what your doing is tuning the mast to suit your sails, not ordering sails to suit your rig.It was one of the most common problems we used to see many customers used to set up their rigs to a given set of numbers then as time progressed & the sails got softer & deeper(slower) but they hadn't thought to adjust their rig to maintain the shape & effectivness of the sails.
*In short yes they can be made to work.
** Try to get a set off a stiffer carbon set up(less tweak required) regards Barry.