I'm currently driving a 79 CDV 7.0, and a 73 Eldo 8.2, I understand the lackluster of a stock 425, and the joy of a 500. Here's how I see it, what I've done, and plan on in regards to my 425. All I've done to my 79 CDV 425 other than buy a preformance tuneup, is ALL new exhaust, headers from cad co, flowmasters, no cats, dual exhaust with H pipe. That woke my car up significantly, because now it can breathe, an engine is an air pump, so it needs to move air and exhaust as easy as possible. The plan is to put in a better cam, a cad co intake manifold, and a Holley sniper efi carb then ill be done. Parts alone I'm looking at about $2500-3k, and labor to help with the efi $200 or closer to 2k if I paid a shop for it all . My exhaust cost me 2k, I paid a shop. Everyone told me to scrap my 425 and go to a 472 or 500, if you build a 425 it will cost the same as a 472 or 500, a 425 will never achieve the same power as a 472 or 500,... all valid points. But where I am its hard to find a 472 or 500 in or out of a car for under $1200-1500, who knows what problems it has ($), money for parts to install and driving, then theres the preformance add ons so its efficient... if you're like me you know the 425 you have been driving it, its paid for, installed,... I dont want a race car I just want a woke car. Even if all you did was open up your current exhaust, a good tuneup, rebuilt your carb, and put in a new cam, your car will be a totally different car, costs the same as doing it to a 472 or 500 but without the extra work and expense; plus you keep the car that much closer to original. Dont get me wrong I'd still buy the 472, but the 425 is a good engine and more than enough, with a little work and money, to make your deville go like never before.