Hi again and sorry for the delayed reply.
As I can understand your frustrations regarding the initial wish to upgrade the T24,it's necessary to make some clarifications:
1. T24 and MM Sterling.,two completely different beasts.Not to be compared in any way.
2.I bought the T24 because it's inherent mod possibilities-body routing included.Frankly,I wanted it for the wood only and this is what I really got,a NTB mahogany construction with a good balance and ergonomy (thank you Jerzy Drozd for the shape concept!).Later on,as the T24 went through different mod stages,it proved to be a great mod platform for everything in the PU/preamps/bridges/strings range of gimmicks.Obviously,it's not yourcup of tea to buy a "comeback" bass just for making it a Frankenstein (like I did).

3.As the ìnfamous,original ABT PUs went back and forth on this bass,I can say that,in fact,they're not as bad as it seemed on the first glance.Neither lacking "versatility".The woodenry,ergonomics and neck confort have their character(s) and it's all about "the beauty in the beholder's eye".
4.For the most comfortable and hassle-free upgrade,I suggest leaving the ABTs on place and upgrade with an onboard preamp of your choice.This option saves you alot of time spent for finding PU replacements and eventually routing the body for adapting some more common PU standardized dimensions.
5.Speaking of the above,you'll have to choose from a rather wide plethora of products.What you'll have to decide is closely related to the character you aim to (keeping the inherent T24 tonals or drastically change the whole story - a good choice can bring out the utmost,whereas an inadequate one can ruin everything).
Feel free to ask further if you're not very familiar with what I already said.