Simple Q&A D&D 3.5 (by RAW) XXVI

[heavyfuel]

A 548

I completely misread your question.

If you enlarge and then polymorph he would now be a medium creature again. He would retain the Size bonus/penalty to Str/Dex.

He wouldn't retain the -1 to AC/Atk, nor the 10ft space and reach because the spell directly link these with the increase in size.

You could cast enlarge person on him again, but since bonus from the same source don't add up, he'd now be a large human as if enlare person was just cast on him for the first time.

Edit: Swordsaged