If he is a 250 lb TE he is going to have to bulk up quick to be an OL, isn't he? I have not studied OL size, but I'm thinking they have to be bigger than that. Maybe I'm wrong.
Depending on his frame and their plans, they could probably get him to 280 in a year. Plenty of ol dont see much playing time until junior year. Tackles may be more like 300, but Tyler Linderbaum at xxxx is 6'3" 290lbs and may be a top 10 NFL pick. He was recruited as a 255lb 3 star.
You never know with 3 star HS kids, and it's not like we have 4 and 5 star kids knocking on our door.
And some end up being doctors, lawyers and astronauts.