Depending on what has to be done to allow for a bigger cam you might look for someone selling a running 460 with all the hardware.
I would recommend talking to "LakesOnly" for quality Ford information.
X2...... And I'll get slammed sooner or later, but.........not to many 390 Jets out there........V-Drive maybe? "Mild Cam" is a relative term in this group. a 305 Comp XM cam is a "mild" cam to many of these guys..............
Good engine, don't get me wrong!
Problem is, these days, it's more scientific than just that. Obviously, cams and lifters need to (should be) be changed together, but the springs need to be at spec for the cam as well, timing set, degreeing in........ In addition,depending how big you go, is there any machining needed to seat the springs, guide clearance, pushrods, etc, etc. FE blocks is yet another i am not real familiar with. But I DO know for a fact they can run and run HARD against the bigger displacement boys!
Your 390 hardware should work just fine for a 428 as well. Both are rare enough these days, so I think you're better off dealing with the 390 myself. At the point of all this, a complete build would be in order , or just run it as it is until it breaks. That's what I'd do....
Ray
