Your weights seam very high. If the Krill is a comp at 33% scale it should be 24 to 26 lbs. If it is heavier than that look at another manufacturer. 31 lbs to me would unacceptable. I have a 106", 35%, SD Katana (wood) that weighs 26 lbs. with 2 KS cannisters. It would weigh about 25 lb on stock mufflers. What makes the Krill so heavy?
The ZDZ 100 should be an ideal engine in that size plane. With or with out cans or pipes. I've been told the NG version doesn't need tuned exhaust and by my experience with my 50NG I agree. The macs pipe gives it a slight power boost but a way better sound.