64 vs 66 e-brake

[closer9]

Hello,
I'm in the process of cleaning up a 66 short frame with the intention of moving my 64 body over. I see the e-brake assemblies are different. My 66 frame has the rod through the frame on the passenger's side, but it's in pretty rough shape and I can't seem to find any other parts to rebuild this. So, figured the 64 brake works and I have new 64 cables, I'll just move the crossmember over. I haven't taken any measurements yet to drill holes, but did notice a set of holes close to the crossmember position on the 66 frame. Then noticed they're is an extra set of unused holes (possibly matching the 66, again I haven't measured) on the 64.

I'm just curious what those extra holes are, and is there any reason I can't just move the 64 crossmember over to the 66? Or are the 66 parts available somewhere and easy to replace?

I had no idea there were some many little differences in the 64-66 trucks till I started this.

Thanks!