To do GLRNET (Graham's) plenum we followed this process (however we are a bodyshop and use 2k paints through HVLP spray guns):
- sandblast
- etch
- high build primer
- wet flat
- base
- clear
- flat/polish as required
It's a bloody tricky job to do with cans. I'd be tempted to advise unless you're getting it done professionally use something like the VHT as recommended above.
You'll be fighting reactions, incompatible paints, at least 4 different types of rattle can at about a tenner a chuck (etch, primer, base, clear) trying to do a 'normal' paint job.