I'm thinking of buying a player who is 77/82 as DT and 43/84 as a LDE. I need an LDE.
Obviously he already has lots of the key skills to be a LDE - strength, tackling, pass rushing, run rushing (?!?!).
How soon will he increase the 43 upwards - quicker than normal. Will it take just a few games playing in the position to gain position exp?

It would most likely take training camp, preseason and then 1 or 2 regular season games.

I do this regularly, veterans will come up to speed at a related position fairly quickly.

Okay thanks

What impact, if any will the weight of the DT have on his actual play until he trims down to size? Anyone know?

Moving to where?
I just moved 2 DTs from DT to LDE and RDE for my 34 Run Stop... I hope they DO NOT get smaller. I INTENDED for 300 LB DEs.

They will change weights if you permanently change their position from DT to DE, but they won't if you merely move them on the depth chart from DT to DE. The only advantage to changing them permanently is getting can experience boost during training camp.

Experience boost?

Experience at the position.

Yeah but I thought that was gained through matches not just training camp