Sheer speculation on my part, BUT I"m guessing that it"s a 1951 TO-20, with a serial number that starts "TO-45XXX".
Case in point: my 1950 TO-20 was listed on the auction sale bill as a TO-30, because the serial number was "TO-30XXX". (The owner told me that himself - he hadn"t owned it for long. I showed him the serial number chart, and the auctioneer announced the correction. Some other folks also told the auctioneer the same thing.)
It"s a little hard to tell from the picture of the "TO-45" exactly what model it is, but Tony"s right - it does look like a nice one.