If I were you I would have someone drill the tank for you. A good local fish store or glass shop should be able to put a couple of holes in the tank for around $50. They may not be able to drill the bottom though(tempered) but could put a couple holes in the corners and you could use plexi or glass pieces to construct overflow boxes around the holes. I know someone who used Lee's specimen containers as overflows around drilled holes.
I had a 55 drilled recently by my LFS. The 3 holes and bulkheads cost $70. A plexi sheet and silicon brought the total up to $100. A new siphon overflow box would probably cost at least this much or more.
