Hi Bones 92, glad to hear an update from you on your 63 Falcon, when they were new they could cruse all day at 55 to 60 MPH, so it sounds like you might be giving away some power yet. Stock these engines had a compression ratio of 7.5 to 1 this tipicaly equates to a cranking compression test reading of 165 psi per cylinder, your numbers are close to this so the difference is mostly likely from having to use the .025 thicker composite head gasket. The combustion chambers could also vary anywhere from 44 CC to 51 CC average was about 46 to 48 CC. Together with the extra 5 CC of the new head gasket this is a sugneficxate loss in the stock compression ratio, optimal would be a 39 CC combustion chamber with the FelPro head gasket or 44 CC with a stock steel shim head gasket. So it is obvious that your loseing a good amount of power here due to less cranking compression, but my guess is that you might not want to do this fix until a later time that's why I made it number 3. There are a few other things that could give you some extra power when working on the head too if your interested.
In summary i think you could get back all most all of that lost power or even surpass the factory power out put, with some more work on these three areas.
1. Check the condition of the timing chain set, a very loose timing chain gives away some power since the camshaft isn't in sync with the crankshaft. This is very common condition on a high Milage engine. See below for simple testing to determine if timing set needs replacing. Some common signs of a loose or worn out timing chain / gear set, Backfiring, Loss of Power, Rough Running, and Noise in the timing cover. From your description of the backfiring this is a sure bet the timing chain / gears needs to be replaced.
2. Rebuilding of the rocker arm assembly. A worn out rocker arm assembly doesn't open the valves fully, which causes a loss of some power, plus extra Noise in operation of the valve train / Rocker Arm Assembly. This also might need to be addressed to quite down most of the rest of the valve train noise.
3. Plus a .025 to .030 or more mill cut off of your heads deck surface to compensate for the extra thickness of the FelPro Head gasket over the stock steel shim head gasket of about .022). This is for sure causing a loss of power due to a less then stock compression ratio.
So if in the future you wanted to do some more work on the 144 to improve its power an driveableity when you have some more funds consider those items number 2. would be quickest job, and than number 1. And later on number 3.any of these three could be done in part of or over a weekend.
1. A Simple Test to check for a worn timing chain / gear set
The timing chain could be worn / stretched and or the cam and crank gears also worn from lots of miles of use. You can test for a worn out timing chain and the gears by hand turning the crankshaft to the TDC timing cover mark then take off the distribtor cap and mark the position of the rotor on the Distribitor body with a piece of chock, now start slowly turning the crank the opposite direction until the rotor starts to move. The lag or difference of how much the crankshaft moves compared to before the Distribitor rotor starts to move shows how much slop there is in the timing chain & gear set. A good timing chain / gear set would not show any lag or difference of the rotor at the TDC mark when you start turning the crankshaft in reverse. The backfire your experiencing on deceleration is an indication of a loose timing chain / worn timing gear set.
2. The noisey valve train / rocker arm assembly is a tip off, probably because it has a lot of wear in the bottom of the shaft from lack of oiling from all the sludge that was built up in the engine plugging up the shaft and rocker arms. You can get a new rocker shaft fairly inexpensive (see link for one example) plus a couple of new shaft end soft plugs this would go quite aways in quieting the clattering rocker arms. Check each rocker arm for excessive clearance on the new shaft as you reassenble your parts, new rocker bushings should still be available also if you find yours are still loose. You can also get a compleate rebuilt rocker arm assembly or some parts from RAU
http://rockerarms.com
After the repair of the the rocker arm assembly so that you have all the factory valve lift / opening the valves fully again would restore some more of that little 144's lost power. Glad to hear that your enjoying driving your Falcon so all your hard work was well worth the effort. Best of luck
New Rockershaft
https://www.rockauto.com/en/catalog/for ... shaft,5680