Please see ASME B16.34. ASTM A 105 and A 350 LF2 are both listed as endorsed valve body materials under Group 1.1. You need to carefully review the maximum service temperature and other service conditions for this valve application before final selection.
For temperature range -20F (-29C) to 100F (37C) you could use LF1... I thought we were talking something like 400degC when you mentioned high temperature service.
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350-LF2 has two different grades, be sure to specify Class 1 for that 'low' temperature range as it is suitable to -50F; Class 2 is only rated as low as 0 degrees.