Someone on the Yahoo list in AUS (can anyone remember Kevin's last name), I believe tried turbo'ing his 5ME... Only to have a BHG occur TWICE after the conversion. I "think" he went 6M after this.
It's doable, but then it's just a matter of time before the motor craps out.
Because of this, I'm leaving the 5ME in my 81 MKI alone. The head has been retorqued already (from 55 ft lbs to 61 ft lbs, and one head bolt was discovered to be loose), so I'm hoping that this will make my motor behave for quite awhile.
I agree w/ the others. It's doable, but why bother.... Go 6M.
Like the 7M, the 5ME also has a nasty BHG habit, and it's just as frequent. The 4ME, 5MGE & 6MGE's are the motors that seem to behave well