If they are single wall rims - in 27" - the ERD is 620mm to as much as 622mm. That would allow spoke lengths of 307.00mm and 308.00mm using 4 cross lacing.
=8-)
http://www.mrrabbit.net/wheelsbyflemingapplications.php
Grab the spreadsheet...the hubs are in the bottom third under pre-1994 hubs.
=8-)
__________________
5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life