well i was kinda in the same spot as your son, i thought my flathead took a turn for the worst and has been kind of a struggle finding parts for it so i got a deal i couldn't refuse on a 318/904 combo but the motor had been sitting outside uncovered for months so the first thing i did was put it on a stand and tore into it and checked to see what all i would have to replaced and realised i would be getting in over my head building the 318 cause not only would i have to rebuild it i looked into everything else i would have to do to make it work and realised i would have to get a new crossmember, rear end, fab a trans mount, driveshaft, brakes and probably new shocks, steering column, cut a hole in the floor pan and pretty much rebuilding the car from the ground up, so needless to say i decided to keep the flatty and if i need more power i can always get a new head,intake,exhaust and be verry happy with the performance a lot cheaper.