The Hornby 50 is a totally new model and is a massive improvement on the old one, although still not perfect is a beautiful model!
The detailing parts from Hornby could be used on the Lima version but you'd need to drill the holes in the bufferbeam for the different pipes. The main differences you'd need to sort for Eagle would be to cover up the roof grille with a plain panel and fit a front end headlight. Any other differences between refurbished and unrefurbished are quite subtle and not really noticable from a distance.
If you decide in future to buy a Hornby 50 i'd think carefully- the couplings on them aren't brilliant for smaller radius curves and mine has been a bit of a problem. The Lima ones can be picked up for bargain prices, most have a good paint finish, work pretty well, look fairly good and will take some rough handling!!!
Signs look good btw!!!