Well for what it is worth, I did the research when I was planning my 71 build (crate 5.7) and decided and am using a Holley Terminator X Max harness and ECU. The main reason/s I decided this were;
1. I am familiar with the Holley software (I have a HP system in my 70 Challenger)
2. the Holley system is very tunable whereas the Mopar one is not nearly as configurable
3. the Holley system will "learn" on its own as does the Mopar system
4. I felt that the Holley system provided many more options (VVT, DRW, various dashes, etc.)
5. Holley has a lot of tech and available resources for when things dont work right, I do not think you will find the same with Mopar.
Regardless and as it relates to the tach issue, I think either or any system will provide a square wave signal wire that can be made to run a tach either with an adapter or directly. Lastly you can always have your tach "upgraded" via one of the instrument cluster repair places (I think you can just buy the new style tach and install it).
Here is a link to site I just found that might be helpful:
https://newvintageusallc.mybigcommerce.com/blog/tachs-tachs-and-more-tachs/#:~:text=Tachometers operate by reading a,of times the coil fires.