Fascinating thread, having spent a little time last year trying to work out what chassis Alfa Romeo were using in the 1981 GP season, and given up though I now have a clear picture of what types were used at various races, I must agree it is probably best not to invent numbering systems post period to save future historians further confusion :-)
According to
HPI VLA451M is still available to use on 'DECADENETFORD' 3000 cc Manufactured in 1974 !