I spent some time to look at different seals, dimensions, etc.
In the end I reverted to installing the same National 3945 seal. I did get an SKF 21771 seal, but it's a tight fit on a balancer without a sleeve, no way it fits on my balancer with the sleeve. The ID of the SKF seal is 2.145".
And with all the documentation I do, I can't find a record of what sleeve I used (Timken or SKF). But in either case, they note that the original balancer seal can be used.
Incidentally, I've linked to the SKF seal catalog, may be of some interest:
SKF Seal Catalog
The OD of the balancer with sleeve is 2.360".
The new National 3945 seal has an ID of 2.245" (measured with my digital caliper) and is supposed to be for shaft size of 2.330". This 3945 is listed for pretty much any 70's/80's truck with a 454.
So doing some math, if the 3945 installed on a shaft of 2.360" and it has an ID of 2.245", that equals overall compression of .115", or a circumference compression of .0575". This should be more than enough to ensure a good grip seal-to-sleeve. Anything more and I'd be concerned about the rubber seal overheating, even with the oil bath (cooling) it receives. Subjective feel of the seal onto the sleeve seems good, not too tight but definitely a positive compression.
Rather than beat the seal on with a hammer, I made an "installer" - not fancy but it should get the job done. It uses the harmonic balancer install tool to compress the seal into the timing cover. That threaded part is a pvc cap for 3" pipe, I just cut the center out of it - it has a nice flat ledge to push against the seal frame. I'll post a picture of it all in place as the seal is being installed.