I'm planning a rebuild for my '68 327.
Can I use a roller cam in an older block?
Where is the best place to get the best parts?

You can use an aftermarket solid roller cam in early block, as they tie the rollers together with a bar. All cam manufacturers have roller cams and lifters for SBC, go with your favorite brand.

THANKS!!! What about a hydraulic roller setup? Will there be any conflicts with stock dimension CAT rods?

Many companies offer conversion kits for a hydro roller cam. They are nice if you are looking for a high lift cam with less duration. But for all out performance solid is the best.