if your swapping the motor, the transmission and t-case can also get swapped in. I would position the motor as far foward as possible. problem is that depending on what year the suburban is, the T-case may not be very desirable. If it were me, I would use the 5.7, 700r4, and either source a D300 or re-use your d20 (if thats what you have)
as for the axles, keep what you have. I am guessing your suburban is a 87-91 frame, the 12 bolt rear is marginally stronger than your m20, 1 piece chromo shafts and your rear is stronger, plus better gear selections and more aftermarket support. The 10 bolt front axle in the suburban would best be used as a boat anchor. small shafts, joints, and ring gear, little gear selection and little to no aftermarket support. (JUNK) your D30 in stock shape is a better and stronger than a 10 bolt.
Now I am making assumptions on your vehicles equipment based onthe limited info you provided