i don't know about the Aussie 2V heads running out completely, it will just get rarer and rarer till it won't be cost-effective to do the conversion
and as to the cost of the crossflow, well, as the tech section says, all of that is still in research and developement, but, when everything is finished with it's testing phase, i'm pretty sure full results will be posted about everything needed to do it, as well as the cost of it
hmmm, Mike, any plans to sell the XF heads, and possibly a conversion on the site once Jack gets done with his project and has the bugs worked out?
as to the strength of the blocks and how much power can be run through them, check
this thread has a bunch of threads and links to follow, but to make it easy, i don't think we here have heard of an engine failing because of the block
good luck
evan