the torque convertor issues are fairly simple to figure out. earlier engines and torque convertors have a smaller pilot area, the machined hole in the crank and the corresponding knob on the convertor. the later engines and convertors have a larger pilot.
so to recap new engine and older trans means you need a bushing to make up the difference in pilot sizes.
next issue is the balancing issue. 360's are balanced externally, so the convertor has to be balanced. since they never put the 360 behind a 904 you will need to find a good trans shop and order the correct convertor. if I'm not mistaken you should be able to order a convertor with the correct balancing and pilot size, but make sure you address both issues with them so you get it right the first time.
on a different note, I'm trying to get a '61 Lancer together and just found that it has a cable operated pedal assembly, if you are going to go with the V-8 you will need a cable and I will need the linkage setup you most likely have. maybe a swap is in order? I'll have to confirm this is the right stuff on both ends so everyone's happy.