Yeah it's possible to disable th V-8-6-4. I had a Coupe with 6.0 litre and they replaced a chip or disconnected a sensor, turning it into V8 all the time mode. If you read the literature for the 1981 Cadillacs they describe it as 'space shuttle technology'. Of course this was before the shuttle blew up.
No, rocker arm or major engine mods are necessary. You might go down to a Dealership that still has someone around who remembers how to do the disable. My 81 had disabled around 1987, so that was a long time ago! Disabled, that 1981 engine gave me 232,000 miles. You'll find the 1980 and 1981 Cadillac engines are vastly superior to the 4.1 litres that replaced them from 1982-1986 and the Oldsmobile 5.0 litre they put in the Broughams between 1987-1989 were also worthless.
Some folks may still value the V864 if it is still operational. As someone whose gone the distance with that engine, I can tell you several things you may want to look at and replace:
1)Throttle position sensor
Replacing really makes a difference in throttle response and performance.
2) Valve cover gaskets
The design for these was pretty bad. Replacing these every 30,000 miles keeps one from breathing in (and losing) oil.
3)Spark Plugs
This engine will go through plugs pretty quickly. Bosch Platinum plugs can be found to fit it and made a big difference in power throughout the rpm curve.
4)Catalytic Convertor
The 1981 convertors clog quickly and choke up the engine. An aftermarket hi-flo replacement will help with the breathing.
Good luck! It's nice to see some 1981s are still on the road!
