Thank you for your reply, DmColonial!
What I can purchase here is a "barra hueca" (hollow bar by the translator); it already has 16 mm inside diameter, that is a lousy 20 ga bore (0.630"), so the main lathe work is outside (easier).
Locally, 1518 steel is 8 times cheaper than T-304 stainless, so if you think it will work SAFETLY, I will use it.

Best,

Jose

Jose M. Fernandez