Can it be done without any problem, if there are problems what are they and are they fixable

Yes definitely possible, although not entirely recommended unless the box is in very very good condition. If you have already bought the box, I would recommend getting it reco'd before converting. I learned the hard way on that one.

So, in summary, T5 EA to EL will fit any of the E-series.

I did it into a EF, box was bullet proof and nice short ratios!!

My syncros did f**k up after 18 months or so..