I'm looking for the same thing. From what I have found the long bolts are the best logs for the 460. If you want to go center rise manifolds the cheapest way is to find some used performance Chevy center rise manifolds and buy the ford to chevy adapter plates.

I'll probably end up getting some of the performance Chevy manifolds JBP sells and run the adapter plates. Probably end up costing around $1500-1700. Should clear the engine hatch and tall valve covers from the research I have done.

Good luck and let me know if you find an alternative.

Pics of the manifolds JBP sells in this thread =>  http://www.socaljetboats.com/index.php?topic=2023.0 .

I know there more $ than you want to spend but from what I have gathered they are really the only option. Unless like I said you can find some used.