Don't pay any attention to the last comment. The oil leak is likely not a big deal. Do you know specifically where it is coming from, it could just be the oil pan. Secondly, yes the gas mileage will suck, but registration and insurance will be cheaper than a newer car and parts and repairs will be cheaper, and a lot you can do yourself.
Basically it comes down to what you need the car for. If you live and work in a city and need to park on the street, or if you know your going to be puting lots of Km on it, then its size is definately detrimental. However, if you live out of town, and are only going to drive it for recreation and less than frequent use, it will be the best highway car you will ever find. Finally lets face it when does anyone really race: off the line at red lights, or hot dogging on the highway. There is nothing foolish about roaring past some rice burner in a real American MONSTER.
I'm the proud owner of a 79 Chevy Impala, its got a custom 355 race engine puting out abou 450 horse, and yes I suppose it will never take a 90 degree turn at more than a few km above the limit, but I have never seen anyone race anywhere other than on the highway or a main thouroughfare like Portage ave. where at the most you have to weave around the occasional car.
The oil leak sounds like a rear main bearing seal. Difficulty of repair depends on how hard it is to get the oil pan off. On many cars you have to loosen the motor mounts to raise the engine and/or remove/lower the front crossmember.
At least it is a 2 door. There is nothing dorkier looking than a grandma-grocery-getter 4-door sedan that somebody has tried to turn into a "street rod". Even a wagon would be cooler than a sedan.
Go for it. These cars are exetremly reliable, and my LTD II has a 351 W under the hood and I haven't found a Honda yet that will take it.
Big deal if it don't handle well, nothing beats a fire breathing, rumbling, big block.
I am not sure if it is too late or not, but I figured I would add my two cents. First, even at $900, you can do better. A friend of mine picked up a 74 with a 460 (for trailer towing duty) with nothing wrong for $800. The a/c was still so cold you could see your breath!
Also, I would get the oil leak checked by a pro, and get an estimate. Even if it is just the oil pan, it can be a big job. I had to replace the oil pan in my 92 Crown Vic, and the cross member had to be moved and all kinds of other hassles. Almost a $1500 job.
Finally, if you think that the poor gas mileage is going to be a minor issue think again. I have an 85 T Bird with a 302. It gets 15 mpg or so in city traffic. I am throwing a fortune into the tank every week.
Last, but not least, some parts are going to be very hard to find.
Let it go.
All this advice---and the dweezil probably never even bought the car! (nor seriously intended to either)
My Grandmother is giving me her 1977 Ford LTD soon and it is in original condition, with 27,000 miles, garage kept, and looks like it did when it was brand mew. It rides better than any new car I've ever been in. I am in the process of finding out how much it's worth. The advantages to these cars, like any other older car is that they are built better (like made of metal other than plastic) they hold up better in an accident, parts are considerably cheaper and you can do most of the work yourself. I would buy this car even though it may need a few repairs. If it IS only $900, the extra money invested may still be cheaper than buying a new or newer car and it won't depreciate as fast (or at all). as a new car. If it's really what you want, I say GO FOR IT.