I have 645MG's on my GeeBee no issues at all with them.
I also have a DLE 30 in my SU26 Put two tanks through it on the ground then completed the break in Flying it (As was recomended to me by supplier ).
You have a lot of air blowing through the Z'ed's cowl so I wouldn't have thought cooling would be an issue, I flew mine all with the cowl on & a much smaller cowl on the SU.
Steff.