Only chainsaw twin ever made was the Echo 62cc, no longers sold here in the US.,.Parts are still available, and D&B engines makes a twin using the crank and cylinders...Pricey parts....
One of my customers made a big twin using 2 Husky cylinders..Made his own case and put two cranks together..Works great.....It CAN be done..Easier to buy one........[8D]
I have a customer's inline twin made from 2 Quadra 50s...Made in Canada, called a Merlin...Heavy and very pricey....Also had an inline twin made from 2 G62...The hardest thing to get right on an inline twin is the coupling between the engines...Most grind a hex on the cranks and use a hex coupler...Precision Eagle twins and a few others were made this way...