Is 1hr 5min transit time in Dallas enough (QF codeshare to QF8)

I am flying from St Louis to Dallas (QF codeshare) then on to Sydney (QF8) in a couple of months - there is only 1hr 5min transit time - is that enough transit time? My travel agent assures me it is? 

I forgot to mention that I am in J (business class) if that makes a difference.

If your (AA?) flight to Dallas is on time, you should make the connection. From experience, domestic AA flights are notoriously late. Can you give yourself a few more hours as a buffer? 

US domestic flights are less reliable for on time performance. I think @sydneykiwi was spot on. I would'nt want anything less than 2:30hr connections, but that's just me. 

I have had similar connection times on an AA flight from Houston. It is possible unless anything goes wrong - I just recently spent the night at the airport hotel.

My experience of Dallas, is that anything under 2 hours means you might get to your flight, but your bags won't. I am surprised your TA thinks this is fine. I'd be getting a different TA......

Why chance it and create undue stress?

I would say it's just possible (but not recommended) subject to your US domestic flight running on time and your bags being checked through to final destination in Australia from your origin point which means you don't need to collect luggage in DFW. In this instance all you need to do is transfer between terminals on the Sky train and there is no security to pass through. 

I just did this today flying in J from Boston on AA and had a good 15 min spare prior to start of boarding time for QF8 with a scheduled 1 hour 15 min layover and my checked bags made it to Sydney with me.

You are taking a pretty big risk though as any delays, even relatively minor could result in missing the connection.

As many have pointed out, it is possible but really does not allow any margin for error, ie, your St Louis flight cannot be late. QF will start boarding 45 minutes before departure so you should be at the gate only 20 minutes after your domestic flight gets in. In terms of transit through the airport, airside, the class of ticket makes no difference. Just to reiterate another comment re what happens if you don't make the connection- last week I was on a First ticket to transfer from NY to QF 8, missed the connection and was on my own after that. It was rather stressful and there was absolutely nobody available for assistance. 

I'd be okay with it but would make sure I had nothing critical scheduled for the arrival day

Unless your travel agent has done such a connection a number of times before, they'll just be looking at the airports minimum connection time and assume that is fine.

MCTs often aren't fine. More so in large airports which can get congested quickly.
If you know your way around the airport in question, the arriving flight is on time, you can move quickly and the terminal isn't congested, it is possible to make a connection like this.
If anything goes wrong, you can easily miss the connection.

Incoming domestic flights typically arrive at one of the other satellites in this very widely spread out airport - there is a connecting skytrain between the terminals but it is a significant ride. I would not leave much less than 3 hours if I was travelling with luggage and I would ask the gate agent to check that the bags appeared in the manifest of the departing aircraft to be sure. The incoming aircraft arrives around 1pm so, even if it is delayed inbound, it is unusual for the departing flight time to be impacted as the turn round interval is very generous. The weather in Texas is often an issue as well. The Grand Hyatt is landside in the actual terminal that the Qantas arrives/departs from and is a very good hotel.

Have done it many times from Minneapolis to join QF8 in around an hour layover with no problems, as many have said, any delay and you are basically shot, so it is not without risk. In the reverse though, transferring from QF7 I always allow around 2 hours at least, immigration and customs at DFW can be unpredictable sometimes.

You'll be fine. DFW is pretty efficient. No need to worry. I'm in and out 4-6 times a year (and yes, if it's a stormy then things, just like here, will go a little haywire). Cheers.