I could only find 690 and 740 HP mentions online for Walter M601 engine used in Let 410 and turbine conversion of Zlin 37 'Bumblebee'.
Wasn't able to track down the 7-tow picture I once saw/had somewhere, but I was told by some guys in Czech Rep, that the record was 12 tow behind Z37T.
I've seen standard radial Z37 tow and yeah, looks good. Using Extra 300 for towing is like using Jaguar or some Lamborghini to pull trailer loaded with scrap metal..
BTW, that OM registration is Slovak. There's one 'company' I remember from looking up stuff online that is freelance towing monster machine for competitions, probably the one in picture. Not that many Z37T around and more in Czech Rep on (everything's) OK reg.