I recently purchased a 75 f250 that had 4v-390. The pistons are marked 410. It is my understanding that these are the 410 pistons that allow low compression 390, shallow dish and valve reliefs. Is it possible to just add a 428 crank to achieve a 410 with 9.5-10.0 c/r? If so is it necessary to have 410 dampener and flexplate or will the 428 hardware work? Another question is can a 428 crank be set up to use 390 dampener and flexplate?

 

To make the conversion, you need the crank, flywheel and dampner from the 428, inasmuch as the 410 and 428 have the same type of balancing system (external). You can use your 390 flywheel and dampner, but you'll have to get them balanced ($$) by a machine shop to be compatible with the 428 crank.

 

You can use the old flywheel and front parts, but they must be balanced, the 410/428 flywheel is a better option and you can buy them new. I got a Billit steel one from McLeod and it also handles the 12" clutch as well as the 11".
Keep the 410 pistons if you can, they are a little pricy, and if they are in good shape, it'll save you some money.
No mater what you do, you really need to have the engine balanced!

By the way, the torque of the 410/428 is great, one of the best truck engines ever!