Cylinder head torque?

Going to change my piston soon on my SMR 450 and manual said this:

37 Nm+90°- 3.8 Nm+90°- 27.5 ft/lb+90°

Does this mean I first torque the headnuts to 37nm and then 1/4 of a turn?

Yep
I don't know if the spec you've given is actually correct, but that's what it means.

Thanks for confirming

Check the manual. I believe the threads also need to be greased. When doing mine I pulled the threads out on one hole. The italian manual was a bit unclear about the type of grease. Just double check.

I found this info in the past here on CH, and wrote it down. UpTite said 58 ft lbs for the cylinder bolts. Also read that noting special is needed to lube the cylinder bolt threads, just use the motor oil you use in you bike.