will the axle handle it or am i going to have to mod chassis to take sierra axle?

Standard 1.8 zetec has 105 bhp. Put 2.0L cams and bike carbs and you will have around 150bhp.

A nice LSD and heavy duty half shafts should see you OK

It'll handle it easily. Don't bother with "heavy duty half shafts" you won't need them.

I've done about 3,000 miles in mine so far....