I've a slightly tatty Mk5 5 in .22 that I've got shooting quite well thanks to a diana seal conversion and a 1/4" stroke increase.

I'm really tempted to shorten the barrel a bit to make it a little more compact and handier (I've shortened and recrowned plenty, so no technical issues), however I've a niggling voice that says I shouldn't be chopping old airsporters up, even if they are the inferior and common-as-muck MK5 variant