Would it be much worse than traveling to a 3rd world country today, though? Granted, typically travelers get some vaccination, but overall, not that many (mostly Hepatitis?).

Yaws and Smallpox, just to name two, are practically extinct today. You will have NO immunity.

Rubella, mumps, chicken pox, lockjaw etc were all common diseases then. Today, we vaccinate against them, even in the third world. You, like all adults, have probably relied on herd immunity to compensate for your fading resistance.

Intestinal disease was common in this era. It's very rare today. You would suffer from it for the same reason that modern tourists suffer in the third world. Tourists, soldiers, and aid workers grin and bear it in comfortable quarters with plenty of clean water. You would be bearing it... elsewhere.

Disease might not take you out, but it would certainly be more of a problem for you than for the natives.

my girlfriend just went to india and got more than 10 different vaccinations and still got sick.