The front sprocket on my 72 T150V needs renewal. Part number in book is 57-4398, which is an 18-tooth. Part number in the book for my 72 T120V is 57-4397, which is a 19-tooth. I might prefer the 19-tooth for the Trident. Part number in my 74 T150V book is 57-4784. Problem is that the only one which I'm sure will fit is the 57-4398, which is difficult to find. What is the difference?
If yours is the early five speed with the Hoffman bearing (11 rollers) the later sprocket from Wenco will not fit without trimming the splines in the sprocket (unless mine was an aberration). It slide right on the 4372 high gear but not the earlier. See my Wenco Framed Triple Racer posting. Maybe the UK sourced sprocket will fit. The high gear seal I.D. changed on the later sprockets. Your early seal will not fit the later sprocket. You will have to replace the seal with the sprocket. The seal supplied is only single lip. Double lip seals are not available as far as I could find. I had to make a new seal holder for a standard 47x60x8mm double lip seal.