Which ever engine you decide on please stick around here and keep us up on your build. Is your goal to smoke your dad's Merc? What engine is in it? If he has gone the 350-350 route, so popular with dads now days, You'll be hard presses to impress him with a six. It can be done but it's not cheap. You will probably have to think about the rest of the drive train. Now what you will be doing has nothing to do with anything that could be called a restoration.
We're with you!
If the 261 or 235 you find has the long water pump you'll likely need to move the radiator forward. If you do that it opens engine choices up a lot to include the GMCs and the 250-292 later sixes which all still have that vintage inline look. If the mere still has a flathead he's toast!
