The cross bar on 7/8th handlebars is meant to prevent flex, and stop the bars bending up and inwards in the event of a heavy fall... in practice I'm not sure how much extra strength it adds, but you may as well retain it if possible...

I would cut one end of the existing cross bar down to the correct length, then file the two sides of the end flat as per the original, and drill a hole... dab of black paint and bingo, you're good to go!

Jx

__________________
"Where we're going, we don't need roads..."

JennyDakar.com