Why not apply the KISS principle? Install a couple of 6" long pipe nipples into the block to space the ends of the flex lines out past the hot exhaust pipe? That's what I'm planning to do when I get around to building my late model 261, which will be closer to 300 cubic inches at the end of the project. Put couplings onto the pipes to duplicate the 1/2" NPT female threads in the block. Use black pipe to avoid the danger of the zinc plating sloughing off a piece of galvanized.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!