Hey Jeremy,yes you have to etch the alloy,a alloy etch such as wattel super etch is a great product and cost is good but there are heaps of etches that will do the job just have a good read of the data sheet to make sure it will do the trick.you only need a light coating of etch,dont load it on as this will cause dramas such as bridging (cracking)etc,you should then put a coat of primer on as this is needed for the topcoat to addhere to.your acrylic top coat will do the job but two pac topcoat would be my choice.it will hold up to all the engine bay can throw at it (heat,oil, fuel)etc.it will be also be a lot better finish such as gloss,and its a lot tougher.make sure you give the etch and also the primer a light sand between coats with about 400 grit.hope this helps ,mono

should come up nice,enjoy