Boy thats a old homemade drive snout, it looks from the pic like the standard 4" snout that will work on sbc and bbc. You will have to buy the correct spacer to line up the snout to the crank. Are you planning on using a harmonic balancer or a blower hub? Do you even have anything other than this old gm diesel truck blower?
If you run a balancer and a blower pulley adapter with a single vee belt groove you will probably need a 7/8 to 1" spacer on the blower. You will need a different idler for a sbc, the one you want is going to bolt to the blower not the waterpump like the bbc one you have.