how bad to replace engine

[truckdude239]

got a 2003 s-10 zr2 4x4 with the 4.3 been over heating alot special when towing started it up the other day and the coolant in the over flow tank was bubbling truck was cold when this was going on coolant full in the radiator, you can see bubbling in the rad also. so we are leaning toward a blown head gasket no water in the oil, intake gaskets where done last year. found a good used engine for $650 with 60k miles out of an express van. i know its now funn but anything i need to look for when swapping these this will be the new car or truck i've done an engine swap in