Dodge 318

I have 2 slants, one an auto and the other a manual. I have several V8's as well. I did a 5.9L swap into my 72 Charger. IMO I would keep the slant 6. Everybody has a V8 these days, how many people still have the slant 6. The slant is a fast peppy motor when it's running right. My slants will go head to head with any V8 all day long.
Just my $0.02
I get it, have been looking into this same idea myself. To not follow the crowd, keep a numbers matching drive train is very appealing. Then I talk to the machine shops and they say I am spending a lot of money for something that I won't get much out of and in the long run won't be happy with. So far I have found two 318's locally. One is the 318 that I started this thread about. I know it's gonna need some work, I just don't know how much yet, but asking price is only $400. The other 318 is in the car of a wife of someone I know. He want's to upgrade her to a 360 and has no use for the 318. The block was rebuilt previously, has a mild cam, new intake, carb, and comes with headers. He is asking $1500. I would rather go with this one, but I have heard 3 times since last summer "I'm gonna start that swap next week" and he still hasn't started yet.

So I respect what you say, and I really have been diving into this by studying the /6 and what it takes to rebuild one. However, in the end, I'm always going to wish I had that V8 rumble.