My '428' is a 390!

[My427stang]

428 / 428 PI/ 428CJ / 410 - 1UB, or 1U

428 SCJ - 1UA

390 - Usually 2T or 2U I think, been a while

However only way to know what you have is by crank number and bore size. You can cheat on stroke through plug hole, but you still wont know bore size.

However, I would say this, if I had a 390, I'd build a 390, if I had a 428 I'd build a 428. The money it costs to bore a 390 to 4.13 (assuming you have a block that can take it) and buy the crank and pistons, would be MUCH better spent on a set of good heads ported to your intended RPM range.

There is no doubt in my mind a good breathing 390 will eat a stock headed 428 for lunch.

However I have one exception to the above rule, if you have the dough-re-mi, stroke the HECK out of the 390 with a SCAT crank , leave the bore stock, AND do the heads and make some serious street power, but the 428 stuff is pricy and not worth that much power-wise

CJ's eat 390's for lunch, but only because of the heads, the exhaust manifolds, and the intake being significantly better designed, the stroke really isnt that much of a difference to change the behavior of the motor. Airflow is where its at