The Nineteen's came with mostly Mercruiser 165's but pretty sure they had the 3.0L's as well. But they also came with OMC's
If it's a 165, you could convert a truck 250 CID engine with the marine parts off of yours. If it's a 3.0L, you can find one of those easy enough. If you have a Mercruiser but find an OMC engine, you have to swap the different parts over or vice verse. OMC and Mercruiser generally did use the same engines, except OMC used a buick V6 for a while as well as Fords. I've never seen a Buick V6 in a Nineteen though