i have a 305 that is seized and a 350 that had some seriouse ring/piston slap goin on can i use the near new crank from the 350 and put it in the 305 block. in other words besides the rods and pistons, can i put everything from the 350 into the 305 block?

 

Yes, the crank even the rods are the same. The only difference is you will need to use a 350 timing cover and ballancer. Pistons and large valve heads are the only things that wont interchange.

 

I have heard that 305 and 350 cranks differ in the size (mass) of the counterweights, even though they have the same journals and throw.

 

from what I have heard they are interchangeable and you wont need a different timing cover but you may need a new damper/balancer.

 

There is a difference in the counterweights, as mentioned above. I would think that the difference is big enough that you wouldnt want to use the 350 crank unless you had it balanced, ie, weight removed, to match the 305 pistons and rods.

 

Oh I believe the rods are the same 305 and 350 so no weight difference there. I am not to sure about the piston weight and counterweight as mentioned above. You do want to make sure they are both one piece or 2 piece rear main seal also. They are not the same and maynot be used interchangeably unless they are modified and or adapters used.

 

the crank throw and journals are the same in the 350 and 305...the rods are also the same...the only difference is the weight....you can use the 350 crank in the 305 once u get it balanced....allthough once u have it balanced you cant use it again in the 350;...unless u wanna weld the weight back on it...i dont even know if youd want/can do that