Yeah if they didn't reinforce the frames they'd ride like crap/wouldn't conform to cen tests etc.
I'm assuming 853 tubes are DT, ST & TT? As far as I know, you can't manipulate 853 enough to shape the tubing, or if you could, it'd make it horrendously expensive.
What you thinking for the build? Fork travel/offset? Could go Rockshox and do another set of retro theme decals...
If you're going with the retro frame decals and chrome-ing the frame, then maybe some Maguras in classic flouro yellow? Lace up some purple pro4's with silver spokes and suitable rims.... Hmmm yes.