Sumpter Valley Railway 250 & 251

Having seen various photos of the SVR 250 & 251, I was wondering about the conversion from using side tanks to tenders. I have seen pictures of the locos on the SVR being used with the side tanks and no tender, picture of what appears to be a freshly painted loco including side tanks with a tender, and obviously photos with no tanks and a tender. I would guess the SVR sent someone to the Uintah to inspect the locos before purchasing and would know and want exactly what they were getting, tight turning high tractive effort locos. Did the SVR therefore originally plan to use the locos as built with the side tanks to maximize tractive effort? I have seen it written that the tanks were removed to increase visibility. Was this a problem that was discovered after a trial period? Why was visibility a problem on the SVR and not on the Uintah. How much tractive effort was lost? And why would the SVR run the locos with the side tanks and a tender? BRIAN