Yep I did that route 3 times (as crew)....to be honest pax were generally ok as most had been advised in advance of a/c change. Seating on the 738 is just as comfortable at on the 763 in economy and premium economy. Business pax who chose to travel on 738 obviously missed out on the business seating and had a reduced service ( ie meals on standard lay ups as apposed to plated meals). As far as I know business pax were offered a free flight to SFB also.
There was no IFE for the economy pax, but portable IFE players were offered to pax who had booked business or premium seats.
As a crew member it was hard work, what with pax queueing for toilets and galley space etc but we managed.
The 738 no longer operates to SFB.