If it's as good as what you say it is leave it alone. If you can't rely on yourself to keep it standard let someone have it who'll love it like a baby and do the right thing by it.
The mere question is bordering on sacrilege, keep it original otherwise you'll wake up at night with cold sweat's at the realisation you've spoilt a decent original motor. As other's have said, buy another one and fit the V8 into it.
dont **** it up, keep it original there aint many series vehicles that aint been welded or ****ed with at least some point in there life keep it original and do it 2 one thats already been ****ed or is ****ed
Being boring, keep it original.
Turn the V8 into a coffee-table, or fit it in a kit car.
Stick the Series in a Vac-Bag or sell it to a museum.
Buy clapped out old Rangie classic & hybrid it.