xb-60 Glenn my understanding is that there where a couple of different 289 blocks forged. The standard block was just that. The 289/ 271 Hp motor was a higher nickle one. I remember this from years ago like some other special blocks. 302 have about 5-6 different blocks with different blends of metal for the blocks. I do know this from a 65 mustang used to race, the stock bottom end will not last long with out 4 bolt mains and a steel crank. If you want to be trick, put aluminum rods in this motor. There is your 7,500 rpm motor block. Control of valve train is going to be high rate springs, top of the line rockers and maybe a bridge support to help control harmonics. IMO solid rollers will make more power overall. flat tappets need wide lobes to do the same thing. output on this motor is still going to be in the high 400 possible 500HP range. Life on the motor is limited to 15-20k miles.
Oil pressure at idle will be very important and doing
oil upgrades to the block and crank/rod bearings. having
oil feed lifters for out the bottom of the lifter to camshaft contact or pressure oiling to the rollers in this kind of lifter. Balance will need to be dead perfect with all componnets balanced togeather. The rule of there is no replacement for displacement works and is just simpler to do with less stress on the motor. good luck with the build Rick L.