I'm trying to get a 99 5.3 to fit into a 72 4x4 350

[The_Noise_Maker]

The truck is a 72 1/2 ton 4x4 auto 350. I'm trying to get a 99 5.3 to bolt up to the stock tranny. Bolt pattern is right on the bell housing & we're thining the cross member for more oil pan clearence. I believe i'm going to have to move the transmission forward because of the heads hitting the firewall. Has anyone put a 5.3 into a 4x4 before? Any ideas besides getting the driveshafts re-cut? Thanks