I'm a believer on running with what you already have - but somethings what you have doesn't work together.
It also appears you are doing things correctly by researching and asking questions. I know of many who jump in blind and are frustrated with the results of un-matched parts and so forth.
The Edelbrock Performer 2176 (or 3776) is a great intake for 318’s. Its also lighter than the cast iron version and is reported to flow better than the factory cast iron intakes.
Note: the 3776 has EGR provision whereas the 2176 does not. There might be a digit after 2176x/3776x if polished or painted.
The Performer RPM is similarly named but is no where close to same intake.
The Performer works best for street driving and might be one of the best “streetable” intakes out there unless you have a really warmed-over engine that can make RPM’s.
The Performer intake will bolt right onto a 318 (small ports) as is. It will also work with 340/360 (large port) heads with a minor modification (remove the lip) performed, first (below).
The 600-cfm carb sounds like a great choice (if mostly stock or mild mods) – but I agree with others, the AVS/Edelbrock Thunder might be a better choice (or, gasp, a Holley with vacuum secondaries – I’m not a Holly fan). Sense you already own the AFB, go ahead and use it for it might work just fine for you.
Keep in mind you will need a longer throttle cable (Pioneer CA-8422, ATP Y-160, Mopar 4027355 or 4306179) and different kickdown linkage to get the 4-bbl to work. Factory 4-bbl linkage is hard to find and sometimes is wrong or incomplete if found used.
My recommendation is to replace the factory kickdown linkage with a cable system, for It makes that aspect a breeze.
https://www.manciniracing.com/retobotokica.html
https://www.summitracing.com/parts/lok-kd-2904ht/overview/ (or similar system).
I like the idea of you using the chain tensioner. I will always install one on any small block rebuild I do. It costs a bit more money and a bit more labor – but it will keep engine timing right on spot.
Note: the double roller timing chain will be nosier than the aluminum/plastic gear version, but it will last forever. The only reason Chrysler used the aluminum/plastic gears were because they were cheaper and quieter. A person could order a HD 318 - with means it comes with the double roller chain, instead of the aluminum/plastic one.
how far down in the hole are the pistons at TDC?
Measure and calculate, re-measure and re-calculate. Do it again if needed. Best to do it correctly and know what you have than to mis-match things and spend forever trying to figure out what went wrong.
Factory “installed piston heights” are inconsistent and almost always leaves the compression ratio less (or way less) than expected. I would bet $5 dollars (if I had it to bet . . .) your existing pistons are not even close to the deck. If crank and pistons are installed, it doesn’t take much to measure 'em. If engine is apart – well, that takes a bit more time to figure it out.
I have seen some factory small blocks, made in the late ‘70’s, that come a good ½” short of the deck. Not saying yours do – but it is always a good idea to measure twice and cut once . . . wait, I’m thinking of woodworking here – but same principle applies here.
BudW