A good starter plan and yes it most certainly CAN work. I run multiple turtle tanks, 2 are 55 gal tanks. After years of mucking about with various filters and DIY filtration setups I can tell you straight off the external canisters are the only way to go with turtles for the long haul. No internal filter has the capacity for the bioload created by a turtle. As a rule of the thumb for turtle filtration always use a minimum of twice the rating for a heavy fish bioload of the same amount of water. A pair of AC70 HOB filters can do a 55 but after years of trial and error I use eheim classic 2217's on most all of my turtle tanks (most bang for the buck IME) they are rated for 159 gallons of tank water (yes I subscribe to the triple filtration school of thought). On the 55 that is 3/4 full the input/output is no issue, these filter come with a spraybar and eheims water column draw is not any issue at all, tank inhabitant - my sons 5 year old male Rio RES. In a nearly identical set up I've got my niece keeping a male concentric DBT, same filtration (I help her with setup and teardown as needed, @ 19 she handles the rest on her own).
On the other 55 in my home (once again same filter) water is only 6 inches max with much of the depth at the 3-4 inch level - shallow depth for spotted turtle group. This system I've run a few different ways - easiest way to deal with shallow water on these canister is to use the eheim pre-filter and anchor it with rocks. The prefilter was necessary when the spotteds were little - or at least needed for my piece of mind to offset the draw, when they were bitty I set it up so that even if one were to somehow get caught in the draw the water level was shallow enough that they could still lift their heads out - never happened, but I was mindful. These days on shallow water draws with that filter I just just reverse the hard intake J tube, attach a length of flex tubing to the short end and attach it horizontally low in the water - no problems.
Spray bars are great with turtles, breaks up the surface tension of the water nicely and prevents the ever so common protein film build up. Water spots can be a real pain but I've found I can minimize both water spots and noise by aiming the spray bar at an angle toward the back glass, allowing it to hit where the top of the water line meets the glass - enough splash to aid in water quality, minimize spotting, and reduce noise a bit.
Over the years many have had success with fluval canisters on tanks at least a bit over half full - the eheims have never given me any problems on turtle tanks, a far cry from other I've used - they are the only kind I'll buy any more for turtles.
F&S has good prices -even better on sale, and all extras and media included (minus the prefilter - but I only ever feel the need for that with hatchlings so I just rotate the one I've got).
link:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=3603