I know next to nothing about 3D printing so keep that in mind with these question:
1) If weight is an issue, would printing a solid block, instead of a hollow 2-piece model, make sense or is that cost prohibitive?
2) Either way, could holes be added to press-fit 1 or 2 lengths of rebar through the brick longitudinally?
Scrap rebar can be found at local concrete precaster and contractor yards. Probably at no charge.
Keep up the good work!