I changed from rope to rubber and found that the rubber was no better than the rope.
for rubber to work in a rope seal housing the housing needs to be concentric with the crank.
which it won't necessarily be if the block has been align bored.
if it isn't concentric only rope will work or you need to do a shimming job on the rubber on the side with most space
best rope seal I had was from bestgasket in the states.
they don't list for 383 400 440 but a 392 hemi one would probably fit. they are generous with the rope
this is a rope seal with a kind of putty in the middle.
you can pull them in if your rope seal housing has not been drilled for a small pin to hold in the current seal or dinged to many times with a punch to achieve the same.
whack in the rope with a big socket until you get less than 24 fllb turning
Force increase on the crank
trim with one of those extending craft knives with the snap off in section blades
rest lolly stick against crank to avoid nicking it
you need a cereal box cardboard of thickness standing proud above cap face or block face
so you cut a section of card the shape of the cap face with a cut out the size of the seal channel to go round the protruding end of the seal.
place it on the cap face
put you lolly stick down the back of the seal against the crank and rest the knife on the card spacer saw away inwards gently until you cut into the stick
its a pain but ive now done it 4 times and to be honest I pretty happy with my performance this last time
Dave