larger inline 6 in the 55-59?

[alden]

Just curious if anyone's swapped out a bigger straight 6 into their taskforce pickup. I really like the look and thought of the inline six but would like to find a more highway suitable platform for some cross country trips down the road; I know it's possible with the 235, this is mostly brainstorming while I wait for various wiring parts to come in

So are there any big GM straight sixes that are common enough to be reasonably inexpensive and also powerful enough to make the swap worth the effort?

Thanks!
Alden