[Fusion_power]

I think you have an error in your description of the genes involved, but will let you work out some of the details. Here would be some thoughts to look at.

gs - causes green stripes. You state both varieties are homozygous therefore can ignore this gene.
gs--green stripe Irregular longitudinal green stripes in epidermis of unripe fruit; retaininng chlorophyll for longer period during ripening, and eventually assuming paler color in fully ripe fruit; changes limited to epidermis. Striping may be observed on stem under conditions of high humidity and low light; heterozygotes exhibit some faint striping on fruit, but scored as a recessive.

el - causes elongated fruit, could be a different gene, there are 7 genes that cause various flavors of elongated fruit, same math so which one you are using does not matter. Please note that TGRC does not describe all of the variants.
el--elongated eElongated fruits as in Oxheart.

Aft - causes petunidin to accumulate in the fruit where exposed to light.
Aft--Anthocyanin fruit Anthocyanin in green and ripe fruit; environmentally sensitive, absent when shaded

atv - atroviolaceum
atv--atroviolacium Excess anthocyanin on leaves, stems, and fruits.

gwr - this is an interplay between the r gene (yellow fruit) and gf gene which is a phytochrome regulator that disables production of carotenoids. Since these genes are presumably already homozygous, you can ignore them.
gf--green flesh Persistent chlorophyll giving ripe fruit purplish-brown color.

gs - causes green stripes. You state both varieties are homozygous but you can't ignore this gene, it tends to do an unusual on/off dance. Most of the time, it will be on since you are using two varieties that are homozygous for the trait. It is a visual trait so easy to select for.

Since you are combining 4 genes, and 3 are from 1 parent and 1 is from the other parent, you should see the desired segregant in a growout of 256 plants. If you choose to grow in 3 seasons instead of 2, then you could do the job by growing a total of 16 plants but with a caveat that it would take an extra generation or two and one extra cross to fully stabilize the variety. Please note that the above ignores linkage. I did not check to see if any of the genes are on the same chromosome. You could take advantage of the fact that all of the above genes are somewhat penetrant meaning they can be visially selected for even when they are heterozygous.

DarJones