How about this from Amazon prime - quick get. Then drill a piece of aluminum scrap plate for tight slide on fit, and finish with some JB weld it on. ??

ICT Billet 5/8" to 5/8" Inch Hose Barb Splice Coupler Repair Fitting Adapter Connector Radiator Coolant Intercooler Heat Exchanger Fluid Designed & Manufactured in USA Bare Aluminum AN627-10A

https://www.amazon.com/Splice-Couple.../dp/B07G3K8L45

Or just mount the plate, then push the hose up tight on the fitting = trapped the adapter in place on the plate.