These cars are known as 4000 lb instant boat anchors. That's how quickly the last 4100 engined car I had took to self-destruct. Just driving down the street to work... Plan on an extra $5000 at some time in your ownership for a new engine. And DON'T expect them to keep their value. Collector's item, yes. Truly valuable collector's item, no.
I have an '81 Eldo, and I took the RR grill off as well as the '57 Imperial type spare off the trunk.
What you might be better off doing is looking for a '78-79 conversion. I just drove my 157K '79 Brougham 2100 miles to the GN and back with no problem. There is a green '79 convertible on eBay right now. The '77-79 engine and transmission are considered one of the finest Cadillac drivelines ever, and with care, are near bullet-proof. Good luck in any case.