I put a VL motor, auto gearbox, dash etc in a VH about 6 months ago. I thought it would take 6 weeks but 3 months later it was finally done. Yes the cat was one of the many little problems along with the A/C, the dash, the radiator, the fuel tank, the auto gearbox rear mount, etc. All of these little problems were expected.
I gotta say it was worth the effort. The VH has done 95,000k, one owner, immaculate condition. It just didn't like ULP and no power steering.