Well...the $1,200+/- cost of plans and materials could go towards getting a proven backhoe meant for your machine, versus taking a chance and hoping this bargain basement approach works. If it doesn't work, you're out the cash and time, and back where you started from.
For occasional excavating work, I suggest you rent a mini-excavator. The last mini-ex I rented was around $200/day as I recall. Mini-exs are fun to operate, and are great tools.