If your shocks don't fit with the truck frame on jack stands and the rear hanging free, I wouldn't use them. You shouldn't have to jack/pull the rear and frame together to make them fit, putting shocks on that are to short could cause them to pull apart if you go over a bump and the truck catches air. Shocks are not meant to be axle travel stops.
Monroe has a calculator on their web page that lists shocks by the compression and extension measurements. The compression measurement is measured with the truck sitting on it's tires minus the distance from the top of the rear axle to the frame bump stop. Then jack the truck up and let the axle hang free, that's the extension measurement. I would find a shock that is a little shorter and a little longer to have a slush factor built in for safety.
https://www.monroeheavyduty.com/dow...-mounting-length-chart-hd-commercial.pdfMike B
