Transom Modification

Ok heres the deal I have a 1978 20ft bayliner Liberty I had no motor are out drive when I got it I have recently bought a mercruiser 350 with mercruiser stern drive I just found out that the gut that had the boat before my cut a bigger hole in the Transom for a Volvo penta drive my ? is how would I go about fixing this so I mount the mercruiser stern drive.
Are is there an adapter I can buy for this

Thanks for your help