Join the Grand Banks owners forum and ask your questions there. You will get far more meaningful and accurate answer to questions about GBs there than you will on a general forum line this. Grand Banks Owner's Resources
GBs are not open ocean boats, they are coastal boats. They are not suited for ocean conditions that might arise before you can run to a safe haven. For offshore work there are far better (and safer) designs.
Ford Lehmans are very old, long outdated designs. If operated conservatively and serviced and maintained properly they are very reliable and can last a long time. They are heavy, noisy, inefficient and polluting compared to more modern engines. While we have a boat with FL120s we would never buy another boat with them again.
Two FL120s in a GB42 are fine if you are willing to cruise at slow speeds, 8-9 knots at best. These engines do not hold up well to continuous running at higher rpm. This means that if you are 100 miles offshore and the weather takes an unexpected turn for the worse, you will not be able to make a fast run to a safe haven. So the weather may well catch up to you and a GB is NOT a boat you want to be in in bad weather on the open ocean.
GBs were designed for coastal cruising and for that they are extremely well suited. As open ocean boats where running to a safe haven may not be an option, they suck and in fact can put you at considerable risk depending on the conditions. They have what many people consider a very poor and uncomfortable ride in rough water with a quite violent "snap back" roll.
If open ocean work was my priority I would not even consider a semi-planing boat like a GB but concentrate on finding a good displacement boat. Willard, Krogen, and some Hatteras models come to mind.