[Rocky 389]

I used the original 1957 timing cover/water pump and had my machinist open the snout hole to take a modern press-in, lip-type seal. If you want to the the 55-59 reverse cooling elbows at the front of the modern heads you'll find the heads are 1/4" shorter that the originals. This is a good thing because it gives you the opportunity to make up a pair of 1/4" spacers for the elbows. After you pop the front frost plugs out of your modern heads, you'll see the elbows line up with the mount holes in the heads but the coolant hole in the elbows is now offset from the cooling holes in the heads. This is where those 1/4 thick adapters come in. I used my "Christmas tree" carbide cutter in my die grinder to "blend" and manipulate those coolant holes to line up better although the coolant has to flow through the dog-leg.
The coolant passages in the newer heads appear to be pretty small but I've had no cooling problems with mine. Coming up on 3 years since I put it together and my car is not babied or trailered probably have 6-7000 miles on the engine now.