well the big red would require extensive modding as far as i know, but the tm 523 is supposedly a drop in motor. that being said, if you had to choose between these two, i would personally want the .28 . but if your buying of the shelf neither of these are a good choice when the lrp .28 trounces the big red, and the picco max .26 has far better reviews and feasibly more power then the tm523. that being said, as long as its not an axial engine your golden.
No Axial are more than just hit or miss...they are greay engines normally for a gallon and a half then they turn to un-tuneable POS. I have had two of then. I know many more that have had them. With all engines there are the few that are just not any good. With Axial there are the few that are good.....very few.
Back to the original question. The 523 is much easier to put in the truck just requires a special mount. The Big Red will be a ton of work to get it to fit propperly. I would personally go with the Picco Maxx .26 over either of the engines mentioned above.
I have a 523 and it never ran right. It had ZERO bottom end torque but tons of mid and high. It was really strange. The Picco was kick butt from day one.
I have 2 rb 523s and a rb 323 they are decent engines if you seal it and keep an eye on the front bearings.good luck trying to find a tmaxx mount very rare.you have to use the rb pipe too they run like crap without it.parts are very expensive,and make sure u use the rb turbo plug also