When you break the neck of a CRT there's normally just a brief hiss of air and a little tinkle of glass. Along with a slightly strange smell. You would be very unlucky to get an implosion or any significant flying glass by breaking the neck.
The V4 and VT4 look very similar except the VT4 had a 13 channel tuner. Same difference as between the V2 and VT2 which are the bakelite cased equivalents. The VT2 was the first 13 channel set because Pye jumped the gun in 1954. Not sure if the VT4 was introduced at the same time.
PS: Jon's pages give the dates:
http://www.thevalvepage.com/tvmanu/pye/body_pye.htm