Where in the heck did you get a bronze
street elbow with a NPS thread? And what makes you think it is
a straight thread? I've only seen NPS on hydraulic elbows only.
BTW- one can screw a straight thread in to a tapered using a sealant
but not the other way around. A tapered hole will crush the male fitting a bit but a tapered thread in a straight hole would go up to the last thread and probably not seal except on the last thread.
In the chart above, if you look at the thread pitch
dia's (e.g. 1") you will see the pitch
dia at the E1 (1.238") of the female tapered thread is the same as the pitch dia of a straight thread. One would have to force it in a little bit but is would hold and seal at typical pipe pressures. Just use RecterSeal #5. See the first line of the last page.