There were a good number of different size injectors for the 71 engines. Each have a number. The higher the number, the more fuel flowed through them and the more HP you got. Make sure all of yours have the same number.
Eagles mostly had the 285 HP version of this engine. The highest factory rating was 318 HP but a 400 HP turbo was a Detroit Diesel factory option, at least for a while and that may explain why the other Eagle you drove seemed more powerful. BTW, if you want a turbo on your present engine, you'll need lower compression pistons. In other words, an engine rebuild. And if you can find a five speed, get it. The only 'problem' is that it has a different shift pattern. First is to the left and DOWN. Second is where first is on the four speed and the rest follow that pattern.
For the gasket, try these...
Jefferson Truck, Trailer and Bus
Address: 1317 W Reno Ave, Oklahoma City, OK 73106
Hours: 8 AM–5 PM
Phone: 1-405-272-0213
Jefferson seems to be closing down so I'm not sure what you'll find if you call them. All the same, try them first.
T & H Bus Repairs
I-45 Exit 264
Ferris, TX 75125
1-972 842-8901
If this is the old I 45 Bus, they should have some Eagle parts available.
Good luck!!!
Stay Fine As A Porcupine!!!///Reste Trés Bien Comme Un Porc-Épic!!!