How about a bar clamp? Like the ones use for woodworking. That would compress the shock to where you could get the bolt installed.
The way I've done shocks before is to cut the strap and stick the bolt in as it lines up the hole. But that's a one time shot, and if you miss you're in your situation.
If the fenders are off, you might try bolting in the bottom of the shock and using your weight to compress the shock to insert the top stud in the bracket.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.