Decided to remove chrome strip and varnish finish on front and rear bumpers and get back closer to original bumper condition.
However brushed on yacht varnish was more difficult to remove than expected, but eventually remove with scraper and 800 grit wet & dry.
Then applied 'adhesion promoter' from spray can. This tended to form droplets rather than a fine even coat. Overcame this by doing a small section at a time and brushing using an half inch artists brush to get a smooth covering.
Then a couple of coats of black primer suitable for plastics. Lightly rubbed down with 2000 grade before wiping with a tack cloth and a then couple of coats of satin black vinyl to finish.
Result looks good so far!