The shocks in your link won't work at all - your 450 has a clevis on the bottom, not an eye.
Similar products are available with a clevis, but there have been reports of interference with the chain guard in some cases.
As for the minimally longer shocks, you won't notice much difference in that context.
However, a pair of twisted rubber bands work as well as stock Honda shocks of that era, so ANY replacements will feel and work better.
I used a pair from an '82 750 DOHC, slightly longer, bolt-up, feel ok (not great, ok).
You can bite the bullet and order some Progressive shocks, which will fit perfectly and work GREAT.
Maybe partially because your wallet will be substantially lighter...........