Actually, the OG is highly dependent upon the brix of the grape-peach juice - presently unknown.
Assume the juice is 19°B (1.078). Four gallons of that juice added to 4 lbs of honey would produce a must whose SG is ~1.104 and volume is 4.34 gallons. Since there was no mention of batch size, I'll assume no water is added.
Using the assumed 19°B juice with 8 lbs of honey yields an OG near 1.127...
