Well, I can tell you that the N3tl flat packs would likly be close to $500 using quality MDF and cnc machined. You'd still need to spend significant time assembling and finishing or paying to have them finished. For less than a $400 difference, you could pick up the CST's in a high gloss black finish, that finish alone would cost more than double the difference !
You'd also have the N3 kit yo u already own you could then sell..... something to think about
Regarding the CSt1's , they do need to have the drivers removed and the poly fill needs to be placed properly as it was installed incorrectly at the factory. this is not a big deal to do.
the CSt's do not use Danny's authentic M130 drivers, they are a knock off that was used to keep costs down and apparently they are very good.
Of course, the usual upgrades of cross over parts tube connectors, and no rez would be benificial but not required.
I had a pair of the N3TL's , fantastic speakers and amazing bass out of that TL