Hi, PK:
If you do the performance modifications to the Ford 2.8 V6, you can get almost as much HP out of it as a stock 289, and it drops right in without any major modifications. This V6 conversion is the only conversion that is available with a complete kit for installation.
The cost is about 5 -7 K, depending on how much you want out of it, it can be done for less if you find the right kind of deals.
V6 Jose, on this forum sells a kit that includes the engine mounts, transmission cross member, alternator/generator bracket, slave cyl. bracket, and custom headers... the kit is about $1600.00, and has everything that you need to do this conversion, and we are here to help you through it.
When I did my conversion, two years ago, I think I started gathering all that I needed in Sept and had the car running in late March. I worked on it almost every day, and never had more fun.
When I had the mufflers installed; on the way home, a guy in a truck chased me down and wanted to know what kind of a V8 I had in my car, and he was shocked to find out that it was this little V6. It sounds great, and runs great.
There are other options that you can do, as well, however more than 100 Sunbeams are running around with one of Jose's kits, and a Ford V6, it is a tried and true method to get some real performance out of our cars.
Take care,