There is probably nothing wrong with using the '68 distributor, and very little but detonation and pinging to be gained by having the distributor rebuilt with a more aggressive advance curve ... on the gasoline available these days! For the 2.4 MFI engines ... T, E, & S engines all used the same distributor! Only the RS 2.7 got a more aggressive advance curve.
My suggestion is to partly disassemble & clean the distributor yourself ... if bushings or new shims, or fiber washers are needed ... you can find them locally and replace them yourself for very few $$$. The following thread has a diagram and discussion of simple distributor maintenance:
distributor lube...