Edit the file \DCS World\Config\View\Server.lua
Min and max FoV are in CameraViewAngleLimits structures, most aircraft will use the default (from default_fighter_player), some have their own values.
Example:
CameraViewAngleLimits = {20.000000,140.000000},
Here Min FoV is 20 and Max FoV is 140
(it's been a while I didn't play with that, I hope they didn't change it).
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EDIT, it seems they changed the way it's done for new aircraft.
For example the M-2000C view settings are in \DCS World\Mods\aircraft\M-2000C\Views.lua
For P-51D the file above should work.
Search for "ViewSettings" otherwise.