I put a 502 Ram Jet in my 70 Convert and realized after I purchased the motor from GM that they used a throtle body from a small block. Will an aftermarket 58 mm throttle body make enough difference to justify the $350 to $550 price?

I wonder if the controller (ECU) will adjust to the new part, the engine may run lean being an open looped controller. You may have to upgrade the controller to something reprogrammable to accept the additional air flow.
We have some experts in this area on board, maybe one will have more to offer.

Leave it alone unless you plan to change the controller. The MEFI 3 has no way to know that you have changed the throttle body and the engine will run lean at WOT.

We used the L98 throttle body because it was cost effective and met our performance requirement for the crate engine.