[67 twins]

I say if you want to go inline 6 go for it. I personally prefer to drive my 250/4speed truck over my 283/5 speed truck.
Might I make a suggestion however? Since you don't already have the engine get yourself a 292 instead. You'll still have an inline 6. You'll have a 40+ cubic inch advantage over the 250. All the same performance parts that fit the 250 will fit the 292 as well. & to top it all off you get a truck engine in your truck. The 292 was the only one of these engines designed solely as an engine for trucks.
That is what I am doing with mine. I have a refreshed 292 that will replace the 250 if I ever get caught up on all those little things that crop up to rob your time.