I owned one up until a couple of years ago,* and I plan to get one again, possibly later this year. The model is much-maligned, but due to come into its own on the classic market, imo. Some analyst are turning around on it as well.
That said, I don't think any project Silver Shadow is worth saving, especially a car between 1974 and 1976. An engine rebuild could run as much as 20 grand, and a used engine would be about 10. The hydraulic brakes and leveling are not that problematic, but years of disuse will mean a lot of work - getting it done would be 2 or 3 thousand, I did it myself with $600 in parts. Because Rolls-Royces are rare, finding shops to work on them can be difficult. However, once you know them well, a lot can be done by the average mechanic at a Shell station. I've walked some through it and all were surprised how straightforward a lot of it is. Personally, I'd rather maintain a Silver Shadow than a 90s 7-series, S-class, or Jaguar.
If your dad is interested, finding a good Shadow and taking care of it would be much cheaper. You can still find good cars for mid-teens, excellent ones for low to mid 20s. The best place to look remains the RROC newsletter, but you can find cars listed in Hemmings,
www.cctol.com, and of course eBay.
epbrown
* My old car, SRX 1327 is in the auction listings of Sports Car Market's January 2007 issue, Kruse Auction. The guy that bought it from me retired to Australia and the person he sold it to just auctioned it for $19,000. I bought it on eBay for $6700, but the next owner did a cosmetic resto.