First, THANKS to David for this quick response. Thanks to you, I got my basic internal engine together today. All that is left is refurbing the accessories and hanging them back on.
To the other poster asking about changing guide rails without disassembling the engine:
1) Are you sure this is an issue in your engine? These things are pretty hardy... my old guides, in a very tired engine, were very serviceable.. if the new guides weren't so inexpensive, I might have been tempted to just use the old ones.
2) Are you having problems with chain noise? It could be that your chain is worn, hence longer length which can't fully be taken up with the tensioner. I experienced this with another engine, and was able to successfully replace the timing chain without any disassembly of the engine (lots of good advice on this subject on this forum)
If you're certain you need to change the rails... my opinion:
a) The upper rail on top of the head, of course, can be easily changed by just removing the valve/cam cover
b) I do know for sure that you can slip the shorter lower guide (lower right side if facing the engine) in and out of the cavity without removing the chain. However, to do this, you'd almost certainly need to remove the radiator and the distributor base housing to get to that guide. Might have to remove the water pump also. Even with that, you really need to get to the guide from underneath, i.e. by removing the oil pan. It wouldn't be a pretty job. Not sure if the longer guide rale on the left would come out with the chain in place.
Hope this helps
Phil/