Unless you have 7000+ rpm on your mind, the crossbolts may be a good upgrade but not required. The 390 blocks split cylinders vertically when overpowered. The mains in a three web 390 will generally live longer than the cylinders will. Every high HP 390 I have ever done eventually split a cylinder. Only one pulled the main apart. I think 600 hp is the limit of the 390 cylinder cores. I think the 428s will go higher reliably. If I were you, why not sleeve the one hole a nice dry sleeve, and then just hone the others.... then buy pistons to fit the bore....less than a crossbolting exercise, and a good foundation....
So Blair, not to hijack the thread but,
What's your thoughts on a 428 A block like I'm putting together ? Cross bolt pro-gram mains, design concept's main stud girdle, .010 over bore, 1 sleave, 3/4 block fill, . If I did my homework and it's properly built do you Think this block could live for a while at 7800 rpm and 725hp ?
