Here's some additional information that is not really pertinent to this thread. Sorry.

A 261 engine (with mechanical lifters) was available as on option on 1500-9500 Canadian Chevrolet/GMC trucks in 1954.

What size is a Canadian 1500 (in USA truck terms)? 2 ton?

So if the 1954 Canadian Chevrolet/GMC Maintenance Manual is correct, then the 261 was available on large Canadian Chevrolet trucks and all Canadian GMC trucks in 1954 (as an optional engine).

Tim