I think that's a good deal and I would do it. I would shop for someone to do the lifter bores. With any type of engine machining I shop for quality of work NOT price.
My first thought was you should just buy an iron block if you're trying to save money, but I do think you are on the right track going aluminum, just for the repairability issue.
You should be able to run mid to high tens with a stock 426 Hemi with a bigger cam and headers if that chassis will hook at all and you run a decent convertor. I would build it once and build it for a bit stronger performance.

Sheldon