I am using a 1991 ram 360 in a street rod build. I was wondering
how to wire in the alt, Is there a way to use an older VR in the system? Thanks for your help!!

you can use either the single field or dual field VR.
there is probably a plug for the field wires on that alt.

just wire those like you would for the dual field or ground one and wire up the other for the single field vr.

I run a 2000 alt from a durango using a solid state 1 field vr.

69 & earlier "box" reg: run blue wire switched ign1 circuit to "ign" terminal on reg. run a wire from the reg "fld" terminal to the alt field terminal (if (1) field terminal). If (2) field terminals then connect this wire to either alt field terminal and ground the other male alt field terminal to the alt case. 70 & up "flat" reg: run blue wire ign1 switched 12V to the top terminal nub in the reg triangle connector with it facing up like a pyramid and T into that blue wire and run it out to either alt field terminal then run the "side" terminal in the reg to the other alt field terminal. A "flat" 70 & up reg requires a (2) field terminal (later) alt unless you grab a brush/brush holder from a spare alt & "unground" the grounded field metal nub end on the earlier alt & likely you can unground it as is by adding an insulated washer so the mini thru bolt no longer lets the brush have contact with the alt case square metal nub that it mounts to, then using a brush/brush holder assy with the male lug for the field wire female terminal to plug into

Very well detailed thank you Robert!!