273 into a 62 Lancer?

1--Yes. The issue is the transmission linkage. I don't know if the critical parts are bolted to the transmission case or are cast into the housing. I'll need a tranny expert to confirm. The front housing (where the torque converter runs bolts onto the gearbox housing. If this is true, then all you need is a front case with the LA bolt pattern. The only thing that may be different internally on the 904 would be the first gear ratio. Depending on what you do as far as throttle linkage is concerned, you also need to address the kickdown linkage.

2--In addition to the points already mentioned, you will probably have problems running dual exhausts. Prior to 1967, the torsion bar crossmember was indented only on the driver's side. You could duplicate the 273HP exhaust or run unequal length pipes that pass through the indentation. Going under the crossmember on the passenger side is going to leave that pipe extremely susceptible to being crushed.

3--Chrysler Engine Swapping Tips and Techniques published by Hot Rod magazine. I don't know if it's still in print meaning you'll have to go to Amazon or eBay to find it.