MSNZ Certificate of Description

[nzeder]

Sure I got the PDF from here

http://www.svra.com/make-model-regulations/

SVRA is Sportcar Vintage Racing Association of USA the only national organisation for Vintage Racing in America.

On their website they have the following statement under the rules/car info section.

"These rules are general in nature and may not apply to every car accepted by SVRA. It is not possible for SVRA to publish rules that accurately define the period authenticity for all eligible cars.

It is therefore the responsibility of each competitor to research the proper period specification for his car, and to present it as such. Supplemental Regulations (Spec Sheet) are published for most Makes & Models and they give specific details on permitted options and modifications. The (Spec Sheet) are to be used in conjunction with the General Rules and Regulations (GRR). When in conflict the (Spec Sheet) takes precedence. The Group Supplemental Regulations (GSR) for each Race Group contains details that apply to that group only and these should also be considered when preparing a car.

Proof of any unusual specification or configuration is the responsibility of the competitor. Updating or backdating within a recognized model (body type) production span is allowed as long as it does not conflict with the group eligibility time period. Continuation cars may be accepted, but they must be backdated to the eligibility period.
These are the resources and regulations that will help you prepare your car to compete with the SVRA:"

Then the sites lists the rules and resources/regulations and links to the make/model spec sheets.

To me this is great method of informing the competitors or those want to compete how a given car should be configured - it does not go into great detail of why these specs are listed on the make/model spec sheet - they are still allowing the competitors to do the research to back up their cars/builds but there is a clear line in the sand statement which is this one

When in conflict the (Spec Sheet) takes precedence

These spec sheet are compiled from know period specifications as raced in the USA under Production Car groups/rules back in the day + as shown in the Ford pdf above they also reference the FIA Groups for the given make/model.