I just bought a 1971 318 Challenger that was originally orange that I want to do an engine swap on. I'm just not sure what direction to go I have most of the top end for a six pack for a 440 just missing the block which is no problem to find. I'm just not sure to build a 440 six pack for it, or a new style 5.7 or 6.2 HEMI for it. what's everyone's opinion ?

By the way I'm going to paint it back to orange and change the hood and wheels.

What do you want from it?
It is your car, your choice, pee on everyone else opinions
Do it your way

if it was mine it would get a stroker 440 6 pack so I could raise heck with the new cars
But it is yours, have fun with it

A later generation modern Hemi (2011 and up) with the overdrive tranny would be a a great powertrain in that car. Lighter, more fuel efficient and equally powerful compared to building a 440. Yes 440s have appeal but the modern Hemi breaths better unless you spend for really good alum. 440 cylinder heads.

Does money or complexity play a role in the decision? One route would seem cheaper and simpler than the other.

The 5.7 is not real expensive and are plentiful. The 6.4s are typically expensive and sometimes hard to find. And the super charged (Hellcat) 6.2 can be even more expensive that the Gen 2 Hemi to buy. Then there's the install costs and that's where the complexity really kicks in. Especially if the original injection and electronics are retained.

Modern engines, like modern wheels and tires on our old muscle cars don't always meet with acceptance.

How about a small block stroker? The car is already setup for one and a 408 with good heads would be a wicked engine for an e-body

This would certainly be the easiest. Although the other options are good ones.

The build for me would be determined on how the car will be used and what you expect out of it. They're all good choices...

what budget do you have ?
any good junkyards, er, i mean, "recycle" places you can browse for what you will need for parts ?
how good are your fabrication skills when you can't find what you need ?
how good are your electrical skills ? this is especially important if you choose to go modern power plant with computer controlled devices you need to integrate with a simple older wiring system.
just a few things i thought of. not trying to say you don't have the skills to do a swap of your choice, just some things that have bit my old bony azz in the past.

Agree.

Step 1 Is answering the above question
Step 2. Is how are you honestly going to use it
Step 3. Answer the budget question
Step 4. Answer 1,2 &3. Then Start putting numbers down on paper. BE THOROUGH. I usually tell people get a catalog form you vendor of choice. Start at page1 and go completely through the catalog writing down everything you want to replace or that will be required. Then add the items not in the catalog, any labor you're out sourcing and total it up

If you do 4 correctly and thoroughly it will help answer your question

In my world, the choice would be easy, but its not my world, its yours.

You are the guy that needs to feed it, and take care of it when your done. Give a lot of thought as to what you intend to do with the car after your drop $20 K into it. A weekly trip to the ice cream store with the wife & kids (or grand kids) is a different build then one competing for trophies at shows, and that build is different then racing to win at a strip, and that is different then competing at an autocross track. Even a get a car out and have fun every weekend can look a lot different then any of the above. Trying to cover them all will only lead to disappointment on all levels.

Figure out what you want the end product to do, then build accordingly.

Its much better to figure out what you want the car to do, and build it to do that then it is to build the car one way, then figure out that wasn't what you wanted, and then try to change it to meet your goals. A car built as an all out tubbed and caged pro street car is not a fun car to go for a 200 mile ride with the family and its vey costly to change it over. What we think doesn't matter at all.

If you are planning on really driving the car a lot then a Gen lll would be the logical choice. If it’s only going to used as a show poodle then I would go for the 440 six pack or a 408 stocker with a good set of aluminum heads.

take step 4 and multiply by at least two.

Wow! That looks like an untouched granny car. I'm surprised it doesn't have the belt moldings on the tops of the doors and around the back edges of the fenders and hood. Looks like it has all the other stuff that would go with that. Probably has AC too. I'd be tempted to just make the numbers matching 318 into a 390 stroker. You'd better look up under the back of it to see what rearend....lol. Don't be surprised if it has a 7 1/4. Was it Hemi Orange or Vitamin C? Cool car to fix just the way you want it.

starting from scratch id be going modern hemi.

I think a modern hemi would be a smart swap. Even a bone stock 5.7 from a truck would be 390HP. If your desires are a nice driving car and not racing using as much factory electronics as you can would net you a great performing car that gets good MPG, great reliability, and you would still be able to roast the tires off no problem lol.

If you are starting from scratch modern power is a good option for any car really.

Especially so if this is ones first attempt, might even go 3X,

Thanks for all the input, I don't plan on racing the car at the track and plan on driving the car lots in the summer on nice days. I enjoy going to a lot of out of town car meets and to local ones as well. Some meets can be a few hours away and i wont be trailering it. It is a pretty low option Challenger with a rebuilt factory 318 auto and 8 3/4rear end. I also have a lot of parts to clone it to look like an R/T including a set of elastomeric bumpers.