AWELCHEL,
Welcome to the site.
Why would you want to change the 6 to 5 lugs? There are alot of aftermaket wheels that will fit your application. You could use adapters to the exsisting 6 lugs to get them to 5 lugs (least cost effictive way).
I like the modern or original straight axel.
The suggestion someone made on here about fitting the engine and trans before removing the cab is an excellent idea...thats a good first start.
good luck and keep us posted.
Dave
Dave