Thinking about this a bit more, a mapping for a factory standard engine would be a useful starting point. However, to quote from the MegaSquirt site;
.... there are a couple of ways to get 'head starts' on things like VE table, etc. One is to use the VE table generator built into MegaTune.
The other method is to copy the setting from someone who has a similar combination of parts. You can look for similar vehicles in the 'Success story' forums. here: www.msruns.com,
However, please be aware that you will have to tune the parameters, even if you are using settings from an apparently identical set-up.