[Safari Larry]

First let me tell you what I've done, what know, and what I suspect. I've closely compared water passages in a '57 (reverse flow) engine with '60 engine (conventional flow) with the intention of converting the '60 engine to reverse flow.

Heads are almost identical. Water passages in the head to block mating surface are slightly smaller on the '60 heads than the '57 heads. It is the block and front cover combination that make the engine reverse or conventional flow. Comparing water passages in the blocks closely, there are two water passages in the '57 block missing on the '60 block (front cover interface). Those passages are for return flow into the front cover / water pump that allow for some water to flow from heads into the block and are also for water circulation in the block when the thermostat is closed. But those water passages can be drilled in the 60 block and you could use a reverse flow front cover to make the engine reverse flow -- except the water passages in the block deck (head mating surface) are different.

In the reverse flow engine, cooling water enters the heads and into the water distributing tubes which will distribute cooling water evenly along the length of the head so the rear gets the same (almost) amount of cooling water as the front of the head. Cooling water exits the tubes directed at the hot spots in the head. Water first cools the head and then some goes into the block to cool the cylinders and returns through two small holes in front of the block back and on to the intake side of the water pump (that water does not get cooled before it is recirculated). The majority of the water flows from the heads directly back to the radiator and gets cooled and recirculated. Because the cooling water is distributed evenly front to back in the head, the water passages in the block are the same sizes, front to back.

In the conventional flow '60 engine (and later), cooling water exits the water pump into the front cover and then into the front of the block through two large holes. The reverse flow engine has these large holes also but they aren't used. In the '60 engine, cooling water does NOT get distributed evenly front to back thus requiring some means to force water to the back. The water passages in the '60 block deck are not the same as the reverse flow block. Front water passages in the '60 block are missing with increasingly larger holes going to the back. The effect of this would be to force the majority of cooling water to flow to the back of the block and up into the heads. I suspect this arrangement of water passages is a result of careful engineering to insure somewhat even cooling of engine, front to back. Water cools the cylinders, flows out the water passages in the deck and into the heads. A majority of the water flows to the back of the block and up into the back side of heads. That water then flows from rear to front of head and on back to the radiator. Forcing water to the back of the engine was not necessary with the reverse flow engine because of the water distributing tubes.

The difference is in the block, not in the heads. No modification of heads (other than the water distributing tube) is necessary to convert a '60 engine to reverse flow. Modification of block is required. I believe a '60 block could be converted to reverse flow but would require machine work to re center a few water holes in the deck. That's why I decided not to try it. But you have a reverse flow block so that isn't relevant to your questions -- it is the background on what I've learned through observation. Back to your questions.

Can heads from a conventional flow engine be used on an earlier reverse flow block without modification??? Yes, '60 heads can be used on earlier reverse flow engines.

Can heads from '61 and later be used on an earlier reverse flow engine??? I don't know, some changes were made from '60 to '61 and I've never looked closely at the later heads. They will bolt onto the earlier block but will the water passages align? Will oil passages align? Are the water distributing tubes required? I think they are required for proper cooling.

Here's what I would do. I would closely compare the head mating surface on later head with an earlier head (or with earlier block) -- by placing a head gasket on each so I could see where things match or don't (take photos to show us). If they match close enough, then you have only the water distributing tube to be concerned about.

You can run a reverse flow engine without the distributing tubes but I suspect you'll have cooling problems which may not be evident until much later or until it has been put under stress (desert, mountains, etc.). Without the tubes I believe most water will flow into the front of the head and right back to the water outlet. The result is good cooling in front and poor cooling in the rear (valves and cylinders). Personally I would not run a reverse flow engine without those tubes because the penalty is too great if there is a cooling problem. If you are making only short trips and in cool weather, it might or might not be a problem. If you try it, let us know if it ruined the engine or not.

Poison, the tubes are made of stainless, I would not use aluminum. I don't know if the water distributing tubes fit in the later heads, that's something to check. I assumed the elbows would bolt onto the later heads but don't know that for sure. If not, using the later heads doesn't seem feasible at all.