No, the short tails are meant to work with the factory 2 bolt midpipe-axleback flanges. The only reason they are even remotely considered a good option is because of the ease of install on stock or stock-location exhausts, otherwise $400+ for a muffler delete is ridiculous.
A local exhaust shop would be able to remove your mufflers without a problem. They will likely have tips you could choose from as well if you don't want to keep the Magnaflow ones. However with the stock resonators likely removed by the custom exhaust I will warn that removing the muffler will likely mean it will sound more loud than clean. I highly recommend sourcing some 12" long 2.5" diameter bottle resonators to replace the mufflers if you want more volume/grumble.
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