[David Hodgson]

Hi Shelley, welcome aboard. You will find endless info here.
There were some celica/supra boxes that would handle a low horse 302 if treated right, but IMHO you are best to take this opportunity to upgrade.
Just about any box will fit in an RMC. If you have a stock 302 and don't punish it a T5 would work but they are getting a bit long in the tooth second hand.

Tremec do 5 or 6 speed box's with variable shifter mounting positions. You can pick the 6 speeds up second hand out of production cars or any of these from Mal Wood Automotive in QLD. Jump on their web site and have a look.

Most guys are building with the T56 6 speed. I'm not sure why, 5 gears is enough for me.