To convert a 70 class Blackstone into a 60 class would involve changing the driver spacing. If you can live with the 70 class driver spacing, you could make one look sort of like a 60 class, plenty of modelers have done similar conversions. If you can pony up the money for a Blackstone its a good starting point, but you're messing with an expensive engine that isn't as easy to redetail as an unpainted brass engine. Backstone made a 70 class with fluted domes and a russia iron jacket. That would be a good start, the 70's came soon after the 60 class so they were both around in the early days.
I'm guessing you are new to all of this, so start small. Have you built any kits? You need to start with a rolling stock kit, like a Rail Line boxcar, or an old E&B Valley caboose or stock car. After a few freight cars, try tackling a passenger car. La Belle kits have been around for a long time, I built a few when I was around 12. Try laying some track, and a few turnouts. Wire up a switch machine. Its tougher than you might think. As suggested, start buying tools . Drill bits. Taps. A scale ruler. Motor tool. My point is develop your hobby skills before tearing into a locomotive. Otherwise, you may ruin your new prize, or become frustrated because you can't do what is needed, like soldering, and burn out on the hobby. Most of us have a box with a ruined engine in it that we thought we could fix or improve, and ultimately couldn't. I sure do. Oh, and read all you can. Get the Narrow Gauge & Short Line Gazette. Study the drawings. Learn how rolling stock is put together. You need to know this if you want to scratchbuild. Realize you will make mistakes along the way. We all do , no biggie, its a hobby. Take the time to learn your basic skills and you will have a pastime for life. I started with then new N scale in 1968, as an 8 year old. I'm now 60 and can't imagine not being a model railroader. Its a great hobby, welcome to it.
brian