Axle dillema

Well..becoming very frustrated. Have tandem axles on a 79 travel trailer I'm wanting to convert to teardrop w/atv platform in front. Problem being, they are "California" style mobile home axles/hubs....can't find bearings etc. so that I can change the hubs out and go with a Ford wheel. So...looking at going to an aftermarket axle...just wondering where I should mount it on the exhisting 17' frame? Should I position it between the tandems that are on there now? or should I just go further back??
Thanks for any help!!
Steve
Thanks for any help!!
Steve