the 4bd1(t) is mechanically the same size as the td5 the hardest parts will be mounting it to the transmission, mounting it to the chassis and then working the ECU to allow abs/ tc keep working.
Im personally now starting research into a detroit 3 53 series and and aircooled Same 4 pot turboed air cooled diesel.
as for the new vs old + repaired head...
short version...
go OEM its worth it for the peace of mind and the warrenty.
long version.
Assuming you mean a driven till it gave up and stopped cooking where the temp gauge lived permanantly in the red and it was shown no remorse and probabley even run without any coolant
Id want to know just how hot, how much warpage the hardness especially around the valve facing and stem junction points. Then Id want a full magnetic flux test done to make sure its not already damaged and Id probabley want a ultrasound to to make sure that theres no obscure densitiy changes near cooling jackets that are just begging to come up and make a crack of themselves.
Assuming the initial warpage was less than say 10 thou and the cam journal warp followed the warp of the head Id look into heat softening and pressing the head back to flat then going onto the next bit. That cams not an itsy bit of proper metal and its not exactly pushing on bic pen springs when its doing its job, especially the injector lobe. I cant see it lasting long if the cam is more than 1/2 its bearing clearance out over its length.
if it was warped and the cam was straight, id use a fine wet grind using a plate stone thats at least 2/3's the size of the head face to bring the face back to flat then repeat the magnetic flux test before bolting it down on a thinsheet gasket on a flat plate bring it up to torque for fixing (using the old bolts) cook it up, give it some pressure then retest. If everything got past all that then ID reharden it, mag test it and install it....
by the time you naff around doing all of that and pay for all the testing (unless you happen to have both boeing and TAE next to your workshop with guys who like to explain how their job works on test pieces or happen to have your own magnetic flux tester, metal ultrasound imager, big enough grinding machines, hydraulic presses, engineering plates your willing to drill holes in to mount up the head to so you can do it on the cheap) its cheaper to get a new head.
If you get a reco head. I still think a mag flux test, ultrasound and a hardness test are mandatory BUT Id reverse the order, hardness test first then the mag flux then an ultrasound.
Id buy an OEM head and refit all the old parts its cheaper than trying to bring broken to the standard I expect.
