As it is only a 2x enlargement you can use your taking lens working as enlarging lens without noticing a flaw in the print. Major issue would be focus flatness, but you can stop severely the lens to gain the DOF that overcomes that problem.
At the end you need only 6 lp/mm in the print, this is resolving 12 lp/mm in the negative carrier plane, so you can stop to f/64 (even f/90 !) for the dof sake without noticing a flaw in the print. (IMHO)
Using the taking lens as the enlarging lens has a wide historic record, of course this has drawbacks compared to dedicated enlarger glass, but IMHO you are not to see that at all in a x2 enlargement, as today you can throw a lot of (little heat) LED light to the diffuser, say 100w led (0r 200), and then stopping a lot for dof.
I used a Sironar-N 300 MC for tests in a DIY enlarger, and it was not working bad at all for x4 enlargements, if stopping enough for focus flatness. For x4 enlargement the lens can be stopped to 45 (or even 64) without diffraction damaging on paper resolution. Nobody can see more than 6 line pairs per mm in a print, even with nose on it, not necessary to speak about it if the 40" print is viewed at the distance that people normally observe a 40" thing.
As you already have your taking lens, there is nothing wrong in to try with it.
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