I would think you should stil be able to use the rod linkage on the 68 tranny. Simply unbolt the linkage from the 68 tranny and bolt up the rod linkage ti the shift lever. I used the original rod linkage from my 67 PG on a TH400. Only diff was gear indicators were accurate. But, trans shifted just fine.
Honest dad, that 455 on the side of the block is a serial number
