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I notice that my link to the assembled engine does not allow the file to be opened in F360 so shout if there are any parts you want the file for. Are you using the free or paid for version?Following on from the cast iron cylinder thread what di you intend to do about the valve seats and guides in your aluminium head as the valves can't really run in that like they would if it were an iron casting.
Try the attached step file for the bracket and if that works I'll export the rest as step files from Alibre as I only do the ones that I want to use F360's CAM for, remember mine are smaller approx 1mm =1/16You could also think about separate cages Loctited into the head to provide a bronze seat and guide