I haven't done that particular job but here's what I would do
That's a long hole. I would definitely bore from both ends. I would start with a 1/4" x 18"aircraft drill For a piece like that, I would use the lathe. First mark and drill for centers. Mount the forearm on the tailstock center and the drill in the chuck with a few inches sticking out. You will need to back out frequently to clear chips. Drill the length of the stick-out and extend the drill a few inches further. Continue this until you have drilled slightly past the half way point. Reverse the work and repeat. The two holes should intersect but most likely won't be completely in line. By extending the drill several inches further, you will bring holes in line. I would do this from both ends. Then I would follow through with a larger drill, 5/16" or 3/8". These holes should be coaxial.
Boring to final size presents a challenge. A .725" hole would require a 23/32" or 18.5mm drill. Finding an extended length drill in either size may be difficult. I have made extend length drills up 48" by making a coupling for 1/2" CRS rod and brazing/soldering or gluing it ti the shank of the required drill. Personally, I would consider making a custom tool. For drilling wood, it needn't be that hard. I would make it with a.single or double cutting edge and drilled for a pilot to follow the previously drilled hole.
When you get to the larger sized holes, you may want to turn inserts for the center to bear on to prevent the possibility of splitting the wood. I would definitely try the procedure on a piece of scrap before I did my work piece.