For starters Cleve, the MRC Tech 2 packs will probably not have enough power to meet the power requirements of a postwar locomotive. I've tried using a MRC power pack and with a modern DC dual can motored loco (no horn, no added electronics) it just barely had enough power to run that with one lighted car.
At one time beginning in the late 1980's before the advent of TMCC, most Lionel trains were being made with DC can motors instead of the more expensive open frame AC "Pulmor" motors. A good many of these locos didn't have horns in them either. The power requirements of these locos versus a typical postwar or MPC-era loco with a traditional Lionel motor are very different. The locos with truck mounted DC can motors run like jack rabbits with a typical Lionel transformer as most have a low starting voltage of 6 volts to the track. The Lionel 1033 and the RW both have variable options that allow a zero starting voltage with a lower high range voltage, which is good for running these basic types of what I call "starter" locomotives.
I will note here, since the advent of command control, even though these locos may also have DC motors, many of them have larger veritically mounted DC motors and with the additional electronics, actually require much more power to run.
I like DC current operation as I run many of these so-called cheaper Lionel and K-Line locos that have truck mounted DC can motors. By removing the circuit boards, I often have more room in the loco to add some additional weight, which allows removal of most if not all traction tires. On shorter length locos, this eliminates stalling. It also reduces the "growl" noise made by dual motored locos on tight 0127 curves, which is made worse by two motors with traction tires on opposite sides of the loco, when going around those tight curves.
I use my old favorite, the Lionel 1033 with a self-made covertor box: Basically a full-wave bridge rectifier with a double post - double throw switch. Lionel also made a covertor box for running their G gauge trains with a normal transformer and I have one of those too. You can still find those on eBay... just look for "Lionel DC."
As Lionelsoni mentioned, there are some drawbacks. Tender whistles is one. But I much prefer off-board sounds, so I took the whistle unit out of a Lionel tender and moutned it inside a Plasticville building running off auxiliary power from another transformer and that suits me fine.
There are some other challenges, but I'm a creative person and part of the fun is coming up with new solutions to these things. I know I'm the odd guy in train world, but I like the way my layout works and I like running the so-called cheaper trains on DC current. Via the 1033 using the A-U setting, my postwar and MPC locos run fine too.
I guess I'm also the odd guy too because I'm happy with my trains and I have no real troubles I can't fix myself. I've had no trouble with DOA locos or service or anything of the like. In my 20 years, I've not once had any of my train locos fail. Given the many complaints and grumbling you read on the train forums about what is wrong with trains, warranty service, lack of parts, or what is/or isn't being made, I am the odd guy.
I've said it before, but sometimes simple really is much better... at least for me. I run trains for fun, not frustration.