Best source for adjustable distributor vacuum cannister?

Please tell me the best source for adjustable vacuum canister. My engine is a 4.9L [yes, I realize wrong forum], but there seems to be more discussion regarding this topic in this forum. My distributor is a Duraspark with a Motorcraft non-adjustable canister.

Thank you in advance.

crane cams used to make an adjustable vacuum can for the ford distributor, check with summit racing, they may have some there.

Any of your parts stores should have the adjustable vacuum advance available.
Then the advance needs to be close to the proper total advance for your engine.
I would bet it would need to be modified for your engine combination as far as total vacuum advance & proper vacuum settings.
But first you need your centrifugal advance set up. Any questions feel free to contact me. Bill

Thank you, Bill!

David