This may be a dumb question but aren't the V8 and 4 cylinder K members the same? What do you think is different? The engine steady rods are different and mount in different holes (both sets of holes are drilled) but I don't usually consider them part of the K member.
The only "arms" that are a different length are the steady rods that attach with nuts & bolts to the crossmember. One is longer and the other shorter but I don't remember which.
You might find a cheap one if you don't need a complete one.
I have a rare NOS vintage center member kit that replicates a 34
type and bolts to 32 rails that allows tran to drop out without need to
remove engine.
If you want traditional function over anal restoration I suggest considering finding a 33-34 center member and welding to 32 rails the old school way.