Crossmember installation

[Weezer67]

I am in need of some clarity. I have a 67 chevy short stepper frame that I am working on. It is a leaf spring set up- 6 lug with a dana rear end. I removed the dana and purchased from Randy a 71 front crossmember complete and a trailing arm frame from a pre-71. The front member is going well but I read that I need 8 grade bolts. Is that corrrect? Any other tips that you could share?
Back to the rear...I cut out the rear crossmember with the trailing arms and I have the crossmember for the spring perches. My big debate is, do I convert to the trailing arm set up or just use the leaf and put the rear on it. The truck will be a nice driver, nothing more. And finally, is it easier to have the axles drilled to the 5 on 5 or are new axles a better option. I read that if you drill a 6 drum axle you have to machine the hubs for the drums? (?) Also how do I tell the machinist what I need?
Any imput from you master fabricators would be greatly appreciated. I value your experience.
Weezer67
Dodge City, Kansas