Converting from 630 to 530 is highly recommended. Back in 1980, chain technology wasn't what it is today, thus the use of big heavy chains. In today's world, super bikes are using 520, or even smaller. There is no reason whatsoever to use a 630 today, other than for an "accurate" restoration.
Since 530 is smaller, you need to move to more sprocket teeth, and more chain links.
Your bike came with a 13T front and 32T rear sprockets, for a 2.46 gear ratio.
To convert to 530, add +3 to the front sprocket, so that means a 16T front sprocket.
For the rear sprocket, you have 16 x 2.46 = 39T (or 38T for a slightly lower rpm on the freeway)
Your stock 630 chain is 84 links. Each link on 630 is 6/8" long, so that means the chain is 84 x 6/8 = 63" long
530 chains are 5/8" long between links. That means you need 63 / (5/8) = 100.8 links (use 102 links, to be safe)
www.z1enterprises.com/530-jtf513-series-...Four/all-models/1980
www.z1enterprises.com/530-jtr488-series-...Four/all-models/1980 
