Manyal brake pushrod length question

1.) Are you using a disc brake master cylinder (large rear reservoir, no residual valve in the port for front brakes)?
2.) Are you sure you have the lines plumbed correctly? (line to front brakes coming from rear reservoir, rear brakes to front reservoir- all via the proportioning valve, of course...)
And yes, the brake pushrod is the same length, disc or drum. But sometimes you still need to use an adjustable pushrod, just because parts have tolerances, and tolerances can stack up- and some new replacement parts don't meet spec to begin with.