Supposedly, in '68, none of the big blocks had the expansion tank, even tho the L-88s did. In '69, SOME of the big blocks had one. I think it had to do with the radiator used for the specific engine. I think the engines with the aluminuminum radiators used the expansion tank, but not the copper radiators. Don't know for sure, tho...the info I have is confusing, at best.

Now I understand, somewhat! 

Here is some more info I found hopefully someone can add it all up and fill in some gaps

|UPDATED|3/28/2013 6:58:40 AM (AZT)|/UPDATED|

Hopefully I'm not being redundant, and more importantly I hope I'm accurate. The early Sharks had a pressurized expansion tank. The radiator and expansion tank caps were not vented as the later ones were, although I believe the expansion tank had a relief function. As water heats, it expands, and level rises in the expansion tank. Taking the cap off of the expansion tank is just like uncapping a hot radiator: it's under pressure, and will flash to steam if over 212F. The expansion line can be hooked up anywhere in the system, it really doesn't matter, as it's just additional volume for the system and keeps the radiator solid. The later ones (74 and up, I believe?) had a siphon/relief type coolant reservoir. Not technically an expansion tank. The radiator has a different type of cap: it both relieves on high pressure, and opens for reverse flow as the radiator cools (and the coolant subsequently contracts, forming a vacuum in the radiator). So excess water is displaced through the cap into the reservoir when it's hot, and sucked back into the radiator when it's cold. The reservoir is not under any pressure and is constantly vented to the atmosphere. Explains the "hot" and "cold" fluid levels on the reservoir. Two different ways of tackling the same problem: water expands when it gets hot. But in the later application, car makers don't have to worry about people burning themselves while checking coolant level. Earlier cars didn't have either one: you simply didn't fill the radiator up all the way. Fill it up too full, and it would relieve out onto the ground (someone mentioned an overflow line straight to the ground: that's it!). Hopefully I've gotten this right. Let me know if I've but out bad info, my skin isn't thin. :) Darryl

Oh: one way to avoid the expansion tank is to install a catch can (vented). Change the radiator cap to a late model one, and buy a cheap expansion tank and run a hose to it. The hose has to go all the way to the bottom so it can siphon back in... I've seen hot rodders use a longneck beer bottle and a hose. It doesn't have to be high tech!

I tried to update the applications if someone sees something wrong please correct

My unnerstanding is that combo will NOT work...as you have discovered. You cannot have two pressure caps in the system.
Bob...I've never seen the longer skinny surge tank...neat! Thanks for sharing that info, too!