Note: I concur with XfbodyX’s comments, above.
I have worked with many a 340, 360 and even more 318’s. I hadn’t seen or heard anything about the early 360’s having thicker cylinder walls. Not saying it’s not true – I just hadn’t seen any differences nor heard anything saying otherwise. It is not worth getting into an argument about, especially if I have zip, zero, nada facts or documentation to prove either way.
I have “heard” the ‘66 and older “Poly” 318’s have really thick cylinder walls (maybe the thickest of all A/LA’s) and can overbore by huge amounts – but the lifter bore holes are not in same area so one would have make a custom camshaft to make one work.
An early (’71-73) 360 will run just as well as a 340 will, if you install better compression pistons, bump the valves up to 2.02”, add a stock 340 camshaft (or better) and 4-bbl intake.
My thoughts:
I also recommend keeping your existing 318 running – until you get your “other” engine built so car has a minimal amount of down time. The more down time usually means the less you want to finish your project.
Find a used 360 magnum engine, using tips mentioned above. You will end up with a nice running engine with the least amount of money put into it. Many things from your existing 318 will fit and work, but some things won’t.
A used 318 Magnum engine has a few less cubic inches and few less HP than 360 Magnum, but still a strong running engine in stock form.
Finding a used 360 pre-magnum engine is a close second. Again, many things from your existing 318 will fit, but some won’t (a little less than what a Magnum will need).
A lot can be done to a 318 (LA or Magnum), as well. Just need to keep compression and other things so it will all work together (instead of having parts fight against each other).
A stroker kit is nice for the extra cubes (and compression) – but those kits also cost more $$$.
I had struggled with this “thought process” after I got my Fifth Ave. The first thing I thought of was building up the 318. A short time later, was getting a 360 and maybe building it up. A bit later I was going with a built 340 (all Chrysler 340’s are High Performance, but the ’72-73 were more ho-hum because of lack of compression, IMO). I might have access to more Chrysler parts than many members have (possibly) and even had a 340 block in my garage at the time (not now), until I decided against that route.
I do have a nice low mileage ’79 360 Motor Home block and a good ‘85(?) 360 pickup block (not a roller lifter block). I even have a ’84 318 police engine as well. All three I have no current plans for – but NV is a bit of a drive to Oklahoma
What it came down to was what I wanted to do. Getting a stroker kit for a 360 and having over 400 cubic engine is great. What I finally decided was to get a big engine bigger so it wouldn’t work that hard, than to make a smaller engine work hard (if that makes any sense). Also I wanted my smile to get close to my ears (when wanted/needed) and going big the only option.
I have two 400 (NOS) big blocks (short blocks), stroker kits, aluminum heads and so forth already in my garage (it is getting a bit crowed in there, sense I also have a 440 Motor Home engine and the ’70 “U” E86 code 440 (out of my 300-H) in there as well as a half dozen transmissions).
Going big block is a whole lot harder than going 360 – sense there is a LOT MORE that needs changing/modifying.
I would recommend finding a machine shop in your area - sense they will be doing a lot of your work. One who has worked on Mopar engines is a huge plus. They might even have a source for a block (or engine) for you, maybe.
We can toss around ideas to you all day long – but this is your project and you have the final say.
BudW