Make body visible in first person?

You could clone the user's body parts locally, then update them (to match the real parts's CFrames) as frequently as possible using Heartbeat. You may need to offset them if they obstruct the camera, and if they exit first person mode you need to make them transparent (or destroy the parts, recloning them the next time they enter first person mode).

Well, to I think you mean you want to Lock FirstPerson mode which you can do by putting this in a LocalScript: game:GetService('Players').LocalPlayer.CameraMode = Enum.CameraMode.LockFirstPerson

But, you wont be able to see your body because its FirstPerson but you will see other players bodys, hope this helped!

local script

char = game.Players.LocalPlayer.Character
game:GetService("RunService").RenderStepped:Connect(function()
    for i, part in pairs(char:GetChildren()) do
        if string.match(part.Name, "Arm") or string.match(part.Name, "Leg") or string.match(part.Name, "Torso") then
            part.LocalTransparencyModifier = 0
        end
    end
end)