Change the filter and add a quart. Using a high quality filter helps extend the life of synthetics, but you are not doing many miles anyway.

70 Go Mango Charger RT
White Vinyl Top
18 Spline 4 speed
Lakewood Scatter Shield/ Centerforce DF Clutch, Hydraulic bearing
505 Stroker, dual 600's, hyd roller cam - 525 hp, 640 torque