I like it!
The 170 has a nice little 3.5" bore which means the valves will come close to hitting the block. The idea is to use the Aussie gasket, and then trial fit the head with the crank removed on a dumy engine, or your one before rebuilding. If you need to relieve anything, it will be apparent if you raise the valves to half an inch and see if there is more than 120 thou clearnace around them.
I doubt there would be any propblem
The 1980 to 1984 heads have smaller valves. The fact that all x-flow heads have valves canted into the centre of the bore means there is less risk of something hitting. This is a standard Cleveland '335', Rat Chevy, BB Ford '385' method of getting excellent power.
On a proposed 170 x-flow, the valve size to bore size is about 1.75:3.5, which is about 50% of the bore. A 4v Clevland head can have a valve up to 56% of the bore size. Plainly, a 170 lookes like a good choice.
Just do be aware that no-one on this forum should make investments untill the details have been proven to work on a 200. Jack has been totally upfront about his aspirations to build a brilliant 3.3 six. The scope of his plans have always been clear.
The time span from idea to completion has involved many scrap engine blocks and no small amount of very talented people welding up a block. So in a sense, the only reason your contemplating this is cause Jack Collins has shared his giant shoulders to stand on.
In the meantime, relax, plan, and know that the heads are only worth what people will pay, and that the longer you wait, the better the chances of a very signifcant sucess with your plan.
I personally think a four bearing short stroke 144 reving to 9000 rpm with a battery of Hillborn injection tubes is my idea of a wild cross-flow. Then driving a 300 hp Falcon would be a huge buzzzzz.
