Coil Spring removal

Recently purchased my dream car 66 289 Conv. I’ve been doing some work on it and have successfully replace the passenger side suspension. No more rattles or squeaks, on that side. Needless to say I had a few close calls with the coil spring. I was able to remove it just fine with some exterior compressors. It was a tight squeeze and they were not exactly on opposite sides of the spring when I removed them.  I uncompressed it immediately after I removed it.
Trying to reinstall with the external compressor was impossible, just not enough room to get it back in. I bought an internal one with the four hooks, but one of the hooks sprung loose mid stream in compressing it, very scary. When I compressed it far enough on one of the next tries, I installed it in its seat and started to decompress it and once again it sprung.  Same problem one of the hooks came loose. Thank goodness it was in the seat and tower correctly and all it did was made an incredible noise and scared me to death.
Quote to do the passenger side is $500.  A lot of money for such an easy job, aside from the spring.
Wondering if it is possible to use the cars weight to compress and uncompress the spring.
With the wheel on, install the internal compressor after removing the shock, and then jack the car up. Then store the spring in a safe location.  Once the suspension is complete, put the compressed spring back in the seat and tower and then reinstall the wheel and lower the jack.. Crazy idea or should I just pay the $500.  
1966 289 2v

I'm not sure which spring compressor you have.  The one I use a is a Cal-Van No. 510 coil spring compressor and it works very slick.  I got it from mustang's plus (you can check out their www and see if it's the same one).  It is an internal 4 arm unit A little time consuming but safe and effective. If so let me know as I've used it with great success.  If It's the same design let me know and I'll be glad to walk you through set up.  

As to using the cars weight to compress the spring I don't think it will work (car isn't heavy enough!) and if it were, it would be VERY DANGEROUS to put the compressor on the compressed spring.  I know I wouldn't want my hands and arms in striking distance!  Remember the power and racket it made when it "sprung"?  Now imagine having your hand in there and getting hit!  BAD BAD deal!  Let us know what we can do to help.  

Sometimes it helps to remove the inner fender coil spring cover on the opposite side of the shock tower inside the front wheel wells. There are 6 or so bolts around the shock tower in the engine compartment that hold this piece on. Once removed you don't have to compress the spring very far to remove it form the spring perch when the cars weight is OFF of the front suspension.
It also helps to put a short piece of heavy chain down through the coil spring and bolt the ends to something substantial on the frame, suspension, etc. so if the spring does experience rapid decompression it will be held in place by the chain as a safety precaution.  

Great points!  I might add that the coil spring need to be clean! (no grease, oil, brake fluid etc.)  As to removing the inner tower panel that's an excellent suggestion.  IF this is a real clean car shouldn't be a problem . ..  but if those haven't been off in 40+ years . .  . you may have another project as about half the bolts will have to be cut to get them out!  My experience anyway!  Good luck!  

The KD Tools compressor that AutoZone or O'Reilly Auto rents works really well.  I bought and subsequently struggled with a $30 compressor.  It slipped and scared me and everyone within a 10 ft radius.  I rented from O'Reilly and experienced what it should really be like.  The rented tool was far superior.  I would not recommend using the vehicle weight.  Too many moving parts.  
Second owner
'66 C Code Coupe
(A Family Affair)

Thanks for everyone’s suggestions. I had removed the cover on the passenger side I replaced, just to clean it up and to help facilitate painting the well. The compressor I had was purchases from AutoZone, and looks like the Cal 510. I have heard of other similar looking ones that come with shims, that mine did not.
I think what happened is that as I was unratcheting the screw (in-between one of the coils with wrench in hand) one of the J hooks must have been pushed and wedged against the well and I forced it off the coil.
I’m just trying to think of another safer way. At the moment I’m going to have to try it the same way and just be more carful.
I may go check out the one that O’Reilly rents.  
1966 289 2v