like eluded to by others, get a real spring compressor, you will need one that is loaded through the shock tops and is inside the spring where the shock goes. you can't use the external spring compressor on it those are meant for McPherson style struts. also there is no room to get 2 external compressors on the spring so it won't work.
one issue with the internal style besides the possibility of slippage is you will find them too long to fit the 71-73 correctly and you will need to shim them with a ton of washers so when you tighten the jack screw it compresses properly.
its funny i have 2 cars like that the compressors are prefect if the access to the spring is either small or really big but there is this middle size that causes the compressor to not work right and you have to shim it. i also have a modern car with a McPherson style strut with the same problem the spring compressor will not get on 4 rings at a time, so it has to be compressed in 2 stages to get it off. takes like an hour to prep one spring to take it out, but it will be much easier on the ford. you will just need to go to the home store and get a LOT of washers to fit the main jack screw on the spring compressor to shim it up so you can compress the spring, when you start doing it, it will make sense.
and the tool can be rented also.
