Trade a tired 327 for a 40k mile 5.0? Free? Sure!
This is an economic win, despite the fact that others will insist the Apocalypse will surely follow if you put a 5.0 in there.
Look, unless you're sentimental about your 327... it is a running core engine worth maybe $150... I know, I just sold two of them last month.
I would trade and enjoy your new engine. You can always build the engine you
want but this seems like a good deal to me.
In the end... your truck, your money, your choice