Stroker Pistons, 318 3.58 stroke?

Pistons for the 3.58, & the 3.79 for the small bore 318 are all custom. AKA Expensive. Though the 4 inch stroke slugs are pricey, they are on the shelf.
Life span may be shorter, but, it isn't like it will last only 5 years and start chugging down oil and such. A lot is how you drive it and how much stress it is under. (Stress = HP torque loads)

The 3.79 used to be the biggest stroker crank you could get. MP had a large verity of stroker cranks.

Build the teen with the 4 inch arm and enjoy. At .030 overbore, with 390 cubes, there's nothing to be worries about.
.060 over = 3.97 bore to equal 396 cubes, if you able through sonic checking and dare go to a 4.0 bore, it now becomes a 402. But that is a lot of overbore for a teen. It is possible.