It's not that complicated. Most heatercores have copper tubes that stick out from them. None have barbs. A few odd ones have o-ring mount types (I'd stay away from those, unless you plan to solder your own barbs).
The tube is best, because you can use any tube, and a hose clamp. You don't have to cut anything, unless the tubes are a bit too long, or they are bent in a weird way.
2-262 click me!
That one might turn out to be a little taller than 7 1/8 inch, because I can't say for sure if the measurement includes the tanks (top and bottom).
If you think you can mod that one, I'll give you a car list.