After a little digging, these are the models I think I have identified. 

1) The pickup for early models 1-5 were electrical switches, whereas the "new style" (BRPE6 and up) had a magnetic pickup - the parts books, etc. make that distinction. 

2) The 28v 1a magnets are referred to as "transistor-driven" and the 115v 150ma ones as "tube driven". I thought I saw one reference to 25ma for the tube-type but that doesn't compute. Also one section of the manual says use a 6000 ohm series resistor, but that should probably be 600 ohms.

Any additions and corrections are welcome!

• switch pickup
• BRPE1 (BRPEB4 base) - 5 level, 11/16" width, 115v 150ma magnets
• BRPE2 (BRPEB2 base) - 7 level, 7/8" width, 115v 150ma magnets
• BRPE3 (BRPEB3 base) - 5 level, 11/16" width, 115v 150ma magnets
• BRPE5 (BRPEB2 base) - 6 level, advanced feed hole, 7/8" width, 115v 150ma magnets
• magnetic pickup
• BRPE6 (BRPEB6 base) - 8 level, 7/8" or 1" width, 28vdc 1a magnets
• BRPE7 (LRXB base) - 5 level, 11/16" width, 28vdc 1a magnets
• BRPE8 (BRPEB7 base) - 8 level, 7/8" or 1" width, 115v 150ma magnets
• BRPE9 (BRPEB8 base) - 5 level, 11/16" width, 28vdc 1a magnets
• BRPE11 (BRBPE6 base) - 6, 7, or 8 level, 7/8" or 1" width, 28vdc 1a magnets
• BRPE15 (BRBPE6 base) - 5 level, 5/8" or 11/16" width, tape notching on 0 and 6th level pins, 28vdc 1a magnets
• BRPE18 (BRBPE6 base) - 6 level, 7/8" width, advanced feed hole, 28vdc 1a magnets
• BRPE21 (BRPEB11 base) - 5 or 8-level, 11/16" or 1" width, 28vdc 1a magnets