Irish Mick,
Checked on your Spencer Carbine serial # 37830. From my list of available Spencer serial #s, the closest I find to your serial # 37830 ARE:
Serial # 37869 a Spencer Carbine issued to Company L, 2nd New York Volunteer Cavalry in March, 1865.
And Serial # 37842, a Spencer Carbine issued to Company I, 3rd Michigan Volunteer Cavalry in June, 1865.
Hope this information is of some value to you. Look forward to photos of your Spencer. Serial # should match - one on the receiver and one on the barrel under the forend.
Two Flints