None of the fittings involved are under pressure, other than the minuscule pressure of the cooling system, so solder will be very secure. All it's doing is preventing coolant from leaking into the crankcase. The fitting that actually secures the copper line has a pyramid-shaped bevel that crimps down on the line as it's tightened into the corresponding taper inside the middle fitting. This is a one-time operation. Once the fitting is tightened it locks onto the tubing and cannot be removed. If you can come up with extra fittings, send them to me and I'll be glad to do the necessary machining and soldering. I would use silver solder (sometimes called "Sil-Floss") that's used to secure high pressure refrigeration line connections. Soft solder will probably work OK, but I prefer a little overkill in situations like this.
Another option would be to use a solid brass 1/4" pipe plug under the pushrod cover, drill a 3/16" hole in it to allow the tubing to pass through the center, and solder the tube to the plug once everything is in place. That would definitely give you more working room under the cover.
Jerry
