If making something as simple as a motor mount is stopping you, then you should probably sell the Olds and use the funds to get an engine that's a bolt in. But if you can weld well, then you should have no issue building or adapting factory mounts.
I start with bolting the trans to the engine and sitting it in the car with trans mount in the stock location. Leave the engine/trans on the hoist, and check the driveline for fitment.
Once the trans is located and the driveline fits, then lower the engine until the motor is level or a few degrees up in front. Then you can look at the factory mounts and see what is needed to adapt to the frame. I usually start with cardboard pieces taped together to make a mount, and once it's right I pull the pieces apart and cut out steel, then weld it all together.
After it's welded together you can install it, and either bolt or weld it to the frame. If I'm welding them or bolting, I still tack them with a welder and then remove the engine to finish welding, or drill and bolt the mounts.
I can usually drop an engine in and fab the mounts in a day without rushing. It's really rarely a big deal unless you're stuffing a V8 into a tiny car that was originally a 4 banger. In that case it took me two days to fab everything for my tiny Austin 4 banger to accept a smallblock Chevy V8.