In addition to fishy's math, and Justin's notable mention of head gasket thickness.
Going from a stock gasket to a thicker one will ad even more of a drop in ratio. This is where we here at FABO say not to do a 360 head swap on a teen. Even more so when the pistons are left stock and the head doesn't get milled.
Now, combine the larger valves which can and normally do cause a lazy air flow. True, it flows more air, but! You will need to get the RPM's up in order to benefit for the potential gain.
So, in the combo of possible problems, not only did you loose some compression when you should be looking for a gain, but the bigger valves moving air slowly dropping fuel out of suspension also lowers HP and torque. This now create's a lazy, soft bottom end and a slower car.
The stock engines already suffer from a ratio to low for use with modest cams never mind a decent street cam. Remember that a typical performance cam has more over lap bleeding compression. Adding a larger cam and the 360 heads just kills the performance of a 318.
Often I recommend staying with the 318 head and porting it out some and sometimes advise on the use of 360 valves. (1.88 - 1.60 ) For the cubic inch size of the engine, a hot street teen can be built with the stock heads ported w/larger valves. While this is a more expensive approach than a straight swap to a 360 head, the performance jump is worthy.
IF there is any question to this or doubt, way back when MoPar had in there catalog a ported 318 head with the note of out performing the 360 head to the tune of 55 HP.
HELLO! 55 HP!
There is a time and place for a 360 head on top. It is build dependent, application dependent.