So the basic Idea is just that Seknu as a servant in the Nasu verse cause I think he would make an awesome Servant, the basic concept I have for him as a servant is that his power is almost entirely dependent on how long he has been summoned for as his power/inventions will increace with time, his main method of combat would be the petrification device used in the Treasure island Arc at least until he has time to develop his inventions.
A title I would give him would be The King of Advancment as for his Noble Phantasm It would have to be either the petrification at the start of the series or some sort of ultimate machine that carries with it the strength of all the work and struggle humanity had to go through to get where it is now as well as their potential to grow and advance.
I think most of his stats would be pretty low (probably E) with Mana and Luck increasing in grade over time and his NP being EX. Now the reason I believe he should start weak with certain stats increasing over time is that it fits Senku as a charcter. He is the culmination of humanity's scientific Advancment, as Senku says himself science became so amazing through the work of many over a long period of time, and in Dr. Stone he accelerates humanity from the stone age to the space stage using that compunding knowledge he little by little grew from starting with basiclly nothing and managed to revive the world (at least I'm fairly sure that's where the story is heading)
I think his class would either be rider for his inventions or foreigner for being in another universe.