How would I know if my 914 is overheating?, Here we go... Options

[1972 914 2.0]

This may sound like an odd and silly question but here it goes:
How do I know if my 914 is overheating?
I just rebuilt the motor over the summer: 2.0L, Euro pistons/cylinders, mild WebCam, new bearings throughout, rebuilt heads, Weber 40s, running 20W-50 Valvoline conventional.
Its a 72 914 with no gauge or anything to indicate temperature.

The reason I ask this question is I've been having some rough running issues lately (past week or two). Before that the car was running an absolute treat.
Symptoms: rough running, hesitant, irregular idle, and it wont rev smoothly.
I think its ignition (just ordered new distributor, coil, and pertronix yesterday) or fuel.

The reason I think its overheating is it seems to run fine for the first 10ish minutes I drive it runs fine and even warms up fine.
And then its like a switch is flicked: I put up to a stop sign or change gear and it starts running like shite.
Either way I'm changing the ignition components but if its over heating then I don't want to drive it until figure that out.

So heres a conundrum for all you teener-heads to ponder while you sneak off to the garage to avoid your relatives on this beautiful holiday. (IMG:style_emoticons/default/type.gif) (IMG:style_emoticons/default/hide.gif)

Oh and Happy Thanksgiving!

[era vulgaris]

What rpm do you cruise at?
If you're regularly cruising below 3,000rpm then you're in serious danger of overheating your heads, especially if you're doing that uphill. Cruising should be done between 3,000 and 4,000 rpm to keep the cooling fan speed going fast enough to cool the heads.

If you get a head temp gauge, I'd highly recommend getting a digital one with a sensor that fits under the spark plug. You'd be amazed at how quickly head temps can change, and the digital gauge shows the exact number so you know for sure.