Engin ID for parts selection

[ctcowboy]

hello everyone new member here. looking for some help. I have a 1969 GMC 2500 step side I need to ID the engine it has a recon engine # 662026 build date 07/24/03 bore4.040 crank size.010 rod size .010 the casting # 3970010 I need to buy parts and am finding that using the model and year does not always result in the correct parts. the casting # helps but it gives me a range of engines. I tried running the serial # number and got no where. as an example the starter is not correct it works but the gap between the starter shaft and fly wheel is to large and it has no shims. this will cause damage over time to the fly wheel. Anyone got any ideas how to reference this number.