I read with great interest Doug Dutra's Aluminium Block Overiew, but are these blocks still available out there? Is the extra time/trouble/money worth it in weight gains vs rebuilding a standard 225?

Occasionally one finds an aluminum 225 "out there". They are definitely uncommon and hard to find in good condition. Only about 50,000 were made between late '61 and early '63. They require special buildup procedures and a special head gasket. The cool factor is there for those of us who are geeks, but they don't lend themselves to high-perf buildups (high compression, forced induction, overbores beyond 0.040", etc.) and no, the 80 lb savings isn't reason enough to go through the extra hassle and expense.

I used to have five of them, now I have two.