yeah it would be no problem to cut a hole and weld a tube in. dont use that tube as the exhaust, always run a separate pipe through it (noise and vibration would be awful otherwise)
also chop the chassis about and box it back up/add extra plate to the sides.
as long as it looks like it will be strong enough it will be.
best option is to go straight through with hole saw and weld a tube in. probably stronger than standard.
i did consider it to get the ultimate v8 sound but had to get practical: extra pipes = extra cost, extra work and most importantly extra weight. as such i had a custom system made to meet my Hedman headers, 2.5" throughout, with Y and single back, centre box only.
tis very lovely!