73 EGR Question

EGR, a couple of vacuum valves mounted on the right side of cowl, and a bunch of vacuum lines under the hood of that 73 are all parts of emissions control and/or spark nock control and not required in most places. Those laws are subject to change though.
If you have the egr port and simply block it off, you have the option of reinstalling the valve if nesessary.
By the way, Fords new 5.0 is reported to be 10.5 to 1 compression ratio.