you can use a AX15 with the 304, if it is a stock 304, you should have little promlems...let me re-phrase that, you should have no more problems than if it was behind the 6 cyl
the 304 from 1971 produced 210 hp
1972-1978 produced 150 hp
1979 produced 130 hp
and 1980-81 produced 125 hp
Considering that the 4.0 HO produces 180 hp stock, and with generous mods can get into the 200-225 range you will accualy be at a loss (Since you said you had an ax15, I assume you have the MPI 4.0)
If that is not enough for you, source a T5 out of a CJ, they are dime a dozen, will handle a built 360, let along a 304 and would be a complete bolt in minus motor mounts and the clocking ring to keep the np231