For some reason Weber never saw fit to outfit these with smoker burners or rotisserie burners so for rotisserie they're not optimal. Side burner or no they were called x50. There was an open cart design for them at one time called x25 and there was even another that was set up as a no lid type (supposedly Aussie type) but I don't know the nomenclature they used for it.
Had a recent conversation with someone with intimate knowledge about the first generation Summit grill in 1997. The big deal with Summit was that it was the first Weber grill with 4 or 6 burners running front/back, not left/right, which made indirect grilling easier. Came with s/s smoke box, thick s/s rod grates, s/s Flavorizer bars, s/s work surfaces.
Here were the original offerings:
Summit 400 (4-burner) and 600 (6-burner) with flat top cooking surface (no lid) and open cart design. Described in U.S. marketing material as an "open broiler" that could "broil enough steaks, brats, chops to feed an entire Boy Scout troop or family reunion in one shift". In Australia, these grills were marketed as the Weber 400 FT and 600 FT (Flat Top) with different accessories, including a Go Anywhere lid for covered cooking on the grate and a griddle in place of a grate:
https://tvwbb.com/showthread.php?54346-1997-98-Weber-Flat-Top-ad-from-Australia
Summit 425/625: 4- and 6-burner grills with porcelain enamel lid and open cart design.
Summit 450/650: 4- and 6-burner grills with porcelain enamel lid and enclosed cart design.
Side burner was an option that replaced the right side work surface, as shown in the link below:
https://tvwbb.com/showthread.php?71400-1997-Weber-Summit-650-in-red
By the way, the sweet red Summit 650 had an MSRP of $3350!
Summit 475/675: 4- and 6-burner version for custom built-in installation.
Dedicated smoke burner and dedicated roti burner came in later generation Summits.
You can see a first-year Summit promo on page 7 of this issue of Grill Out Times News, Winter 1997:
https://tvwbb.com/showthread.php?50978-Grill-Out-Times-Volume-03-Issue-1-Winter-1997