[Rory McNeil]

The 66-67 390 engine is a good combo for Stock, but the 68 doesn`t get the better PI intake and 735 Holley carb the earlier cars can use. A 68 Mustang can be converted into a 67 however. The 428CJ is a good combo too, there are plenty of strong running 428 Mustangs in B&C/S, both stick and auto., despite constant HP factoring (over 40HP from the factory rating).
A 390 would easier & cheaper to get blocks, cranks, and factory heads for, although both the 390 & 428 can run the NHRA legal Edelbrock heads, with a HP penalty of course. Like Jeff mentioned, the FE blocks CAN be a weak point. A 390 should be fine, but over the years, I have had several split cylinder walls in non filled 428 blocks (no problems with Hard Blocked blocks) The current 428 in my bracket car had fairly decent sonic check numbers, but it split 2 cylinders in 2007 before we finally filled it with Hard Blok. I guessing because of the block being over 40 years old, it may have had rust pitting issues on the backsides of the cyl.walls. Another concern, more so with the 428`s longer stroke and higher power, is the splitting of the main webbing. The previous 428 was in my car for over 10 years, but towards the end, the oil pressure kept getting lower, especially at idle. When I took it apart, the main bearing bore webbing had cracked thru the oil feed holes between the cam and crank bores at #2 & #4. That may have caused a very slight amount of oil bleed off, but the main reason for the low oil pressure was that the #4 cam bearing had walked foreward, causing a major internal oil leak. It`s not uncommon for the main bearing caps to show signs of fretting from the caps moving around some. Cross bolted main caps, like the Ford 427 uses would greatly reduce the fretting and main wb cracking issues.