No, it won't be 60 torque on the dial. The -34 engines have been chosen because the -27s are out of production - the -34 is the only small PT6 still in production, thus the only engine available as new/zero time.
The flat rating will continue at 620 SHP, same as horsepower remains flat rated at 620 SHP on existing series 300 Twin Otters that have been retrofitted with -34 engines by STC. The horsepower limitation is an aerodynamic issue - the fin and rudder are not large enough to handle an asymmetry greater than 620 hp. This is why the -27 engine, which has a thermodynamic rating of 680 hp (equal to 53.3 pounds of torque) was flat-rated down to 620 at the start of series 300 production almost 40 years ago. You will note that the series 300 aircraft have the same size fin and rudder as the original series 100, which was equipped with 550 horsepower -21 engines. Rudder travel was increased on the series 300 and additional vortex generators were added to the fin (above the horizontal stabiliser), but the greatest asymmetry that the engineering flight test team could accept was 620 hp - hence that red line at 50 torque that we all know so well.
Trust me on this one, I was there in Victoria at the operators' conference when the Series 400 was announced last September, and there were lots of questions about this exact issue posed to the Viking engineering staff by the attendees at the conference.