R-blocks are a based on a rhombicuboctahedron with square openings cut through 18 faces. This provides many locations and orientations to connect the blocks together with small square pins. A corner pin is useful for supporting the inside corner where three blocks meet (shown in the renders as blue).

Print on one of the triangular faces connected to the internal column to avoid needing supports. The STL should have the correct orientation for printing. Depending on your printer and bed, a small brim may be required. A 0.2mm layer height works very well for me so far.