Sell the custom PC, sell the Mac Pro 1,1 and get a Mac Pro 4,1 or newer. And continue with the project.
That is the last thing I'd do the MP 4,1 or new holds no interest to me at all. The tech is old and the price is new even if used. If I were to do that I'd keep the Hack it's faster and quieter than and single processor MP and most DP's.
when there is a new MP then I'll bite until then I'll entertain myself with oldies.