Dunno what their 'kit' is, but it may be similar to Crane Cams' adjustable rocker assembly that allows Boss-type adjustable rockers or full-roller rockers to be added to non-Boss heads without machining your std heads or replacing pushrods. The Crane setup is routinely used on 351Cs with good success, as long as the installation is done to the letter of the instructions. Failure to use Lock-tite on the fasteners as directed or not torquing the assembly correctly will buy you a fair amount of trouble in a very few miles.
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