Others have used copper pipe &/or fittings to make the repair there, so you should be fine.
I wouldn't eliminate the cross-over pipe. otherwise, the exhaust system might be a tad restrictive.
On my 81 KZ650-CSR the pipes are a pretty small diameter just before the mufflers, so blocking the cross-over would restrict the air flow quite a bit.
1981 KZ650-CSR. Competition, Sports & Road.