Going to use an SVX engien as an example here. The idea is that we want to at least inpsect various areas, and also we want to replace things now , rather than later, while it is easy to do, with the engine out of the van. We want to take care of critical things, lfor example....... the timing belt and the roller wheels that guide and tension the timing belt....want to do those things to protect our investment.

One thing that can happen is that as you do a few parts, you see that related parts should also be replaced at the same time. Say you do the timing belt and tensioner - well.....in order to replace the water pump later on, you'd have to do the timing belt job over, more or less....so it justifys putting in a new water pump at the same time. Then you reliaze that you should also check and maybe replace the camshaft seals, since they are behind the cam sprockets for the timing belt, and it's better to do them now while you are in there.....each time you do a few things....those things tend to advocate for a few more things.

The major areas to address are : Timing Belt area, head gaskets, various seals, and maybe spark plugs. Following is what I recently did to an SVX engine to get it ready to send out on the road for a customer :

replace both head gaskets

clean block & hed surfaces before intalling new head gaskets

clean cylinder head bolt holes in block prior to gasket installation

replace cam shaft seals, left and right

check funciton of timing belt tensioner, replace if neccessary

inspect all 5 roller wheels and replace as neccesary - one by the water pump wears the most

remove oil pump, tighten screws on back, might want to replace o-ring there

replace crank shaft seal in oil pump, reseal oil pump to block

replace timng belt ....be sure to torque crank pully bolt correctly

inpsect and maybe replace rear main oil seal at flywheel end

remove plastic 'oil plate' at flywheel end, replace with newer metal style one

remove thermostat and test in hot water, or install new thermostat, OE type only.

drill a small hole in edge of thermostat to increase flow before t-stat opens

drill and tap water manifold to accept Vanagon temp guage sender

inpsect spark plugs, replace as needed

cut metal tab/brackets of left heater hose pipe by engine plugs.....to reduce clutter

install oil pressure sender at oil pressure outlet, with 'T' so O.P. warning light still works too

replace small coolant hoses to throttle body

replace all spring type hose clamps with German screw type ones

consider replacing hose buried under intake manifold on right side of engine (vanagon rt. )

modify throttle cable bracket to accept non-subaru throttle cable

reseal oil filler tube to valve cover with Toyota black sealant ( I sell it, btw )

reseal valve cover gaskets with Toyota black sealant, or replace valve cover gaskets

might want to shorten oil pan & oil pick-up tube now - can do nicer job io it after engine is installed in van......better to shorten pan as little as possible.

install Adapter Plate, flywheel,with spacer and special bolts, and clutch disc & pressure plate

any small adjustments to brackets or whatever that you can do to make the engine easier to work on. The Japanese seem rather bracket-happy....some of them make sense, some not. Basically 'clean things up' where you can.

there's more.....just need to remember what they are...it goes on and on.