If you review Jim Coffman's MFG Boats website, he has a page located here that contains some historical information about the MFG Corporation and the MFG Boat Company. In that site, Jim points out the fact that MFG Corporation never intended to get into the boat business. They wanted to make fiberglass hulls for other companies.
It is unclear exactly the relationship between MFG Corporation and a company named Anchor Reinforced Plastics, Incorporated of Hazel Park Michigan. One of two scenarios is possible. Either MFG bought Anchor, or MFG spun off Anchor. What is known is that at one point it was called Anchor Reinforced Plastics, and at another time it was called the Anchor Boat division of MFG Corporation. Based on dates of production for the Pintail, it is very likely that MFG Corporation bought Anchor Reinforced Plastics and created the Anchor Division. This is because Pintails were sold under Anchor Reinforced Plastics in the 1960's, but later advertisements referred to the Anchor division of MFG.
In addition to the Pintail, one of the boats that were sold by Anchor was the 16 foot Teal, sometimes called the Teal 16. The sail logo on the Teal is distinctive and very much in the style of the Pintail, Whistler, and Redhead. The logo is easily identified as it has a large block capital letter (P, W, or R) and a bird (perhaps some kind of goose?) in flight passing in front of the letter. You can see examples of this logo elsewhere on this website.
Given the similarities of these logos, it is logical to assume that the Redhead and Whistler were also made or sold by Anchor Reinforced Plastics, perhaps under the name Anchor Boat Company.
Given that the Teal and Pintail were available in the 1960s, and the major boats from SailMFG did not appear until 1969, it is likely that the deal with Anchor was established before MFG decided to get into the boat business with its own brand. But eventually it did create the SailMFG brand.