Very Old Texas Instruments IC's

Hello, I've come across some old TI IC's that I'm hoping someone out there can shed some light on. The date codes on the chips place them in late '67 to early '68. The part numbers are: SN1286 SN1287 SN1288 They are in 24-pin dual-inline plastic packages. The pin spacing 0.10 inch between pins, and 0.50 inch between the rows of pins. These three chips are on a board that is populated with SSI DTL & early TTL devices in the SN15xxx and SN58xx DTL families, and SN74xx (only SN7474) TTL devices. All of the SSI stuff has date codes ranging from 6742 (week 42 '67) to 6804 (week 4 '68). Can anyone out there shed any light on these old devices? Yes...the board with these chips on them is from an old Singer/Friden calculator. Thanks, Rick Bensene The Old Calculator Web Museum http://www.geocities.com/oldcalculators