Those pistons are standard, plain-jane, cast 318 pistons.... meaning they will be standard 318 low compression with a stock stroke crank. If you put a decently large cam in with these pistons and a stock stroke, the low RPM torque will be crappy to non-existent, and that is not what is desired for standard street driving. That is the problem with these and any low compression pistons.
Let's back up and find out what you want to achieve with this:
- 'Street' can mean a lot of things. Is this a daily driver, or a stout street cruiser? Or do you want something with a lot of HP? That will drive the direction of the parts selection.
- I take it that by saying street, you are not intending on racing this?
- Do you have a rough budget range?
- Do you have any option to switch away from a 318 to a 360?
Is there some particular concern over turning down the present crank? Doing that is a perfectly normal and OK thing to do, even for high HP build.
The most common stroke option would be for 4" stroke. The minimal cost for a new 4" stroke crank is around $300-350. (Eagle brand.... some reports have been around of breaking such cast Eagle cranks but I don't know the full history there, so take it with a grain of salt.) The pistons to work with that and using the standard 6.123" long SBM rods are completely different. Here are some:
Chrysler Dodge Mopar 318 Flat Top Pistons | Campbell Enterprises
There may be some combinations of other pistons and Chevy rods that will work, but you will need to turn the new stroker crank down to 2.100" rod bearing journal size to work with the shorter Chevy rods (again, not a big deal). The Eagle catalog has a list of 2.100" journal Chevy rods; they mostly use .927" diameter piston pins, so they won't directly work with SBM pistons that use a .984" pin. That is typically the biggest challenge in finding alternate pistons for SBM's. And, there are not many stock pistons round of any type for the diameter range of the 318 bore. So the easy way is to spend the $$ and get the pistons like shown above with the right bore and pins, and the compression height set up for 4" stroke.
Once the piston/stroke combination is set, then the compression ratios can be calculated, and the heads and cam can be worked upon.
