??? SINCE WHEN ??? He is talking about a 77 LA block and heads, NOT a magnum and NOT a roller.
So far as I know, ALL SB LA repeat LA pushrods with factory not adjustable valve gear are the same length.
http://www.summitracing.com/search/make/CHRYSLER/engine-size/5-9L-360/engine-family/Mopar-small-block-LA/Brand/Sealed-Power/Part-Type/Pushrods-Assembled/?Ns=Rank|Asc
I've had the very same 273 factory stock adjustable pushrods on ever LA small block there is. 1 They came off a 273. 2 Ran them on the 340. 3 Ran them with the 318, and now, 4 on the LA 360 in the 67