I recently was gifted  the "1974 Pontiac (350 & 400 V8 Orange Engines) Chassis Shop Manual Supplement" This manual verifies the use of the 400 sbc in Pontiac B Body Wagons made in Oshawa.

This has been a question about the use of the 400 small block in the B body line that we have not been able to confirm until now. The book is dated January 1974 Oshawa, Ontario. The engine specs are as follows:

400 V8 4BBL Single exhaust

180 Net HP @ 3800

290 lb ft @ 2400

RPO LT-4

There are 4 versions of the small block in this book as follows:

LeMans RPO L30 145HP 350 2BBL auto & manual
Pontiac RPO L30 145HP 350 2BBL auto
Pontaic RPO LM1 160HP 350 4BBL auto
LeMans RPO L-48 185HP 350 4BBL auto
Pontiac* RPO LT-4 180HP 400 4BBL auto

* "B" Wagon Only

Just my observation in the charts, 'Pontiac' refers to the big car or B body line and 'LeMans' to the A body line. It does not imply that a LeMans is it's own marque.

Models covered are Domestic Laurentian, Parisienne Brougham, Catalina, Le Mans, Le Mans Sport and Luxury Le Mans

I hope this is helpful information.