I don't know of a spacer, but I haven't looked that far into them. The spacers I've seen are for adapting older T5's to vintage 3 and 4 speed bellhousings.
I don't claim to be an expert, I'm just posting here what I actually tried myself. I know other folks here have used the V6 T5's and I recall one complaint about a clutch cable running directly into a long tube header. I'd kind of prefer the actual folks who dealt with those particular problems chime in, but you can't relay on any certain person being online or reading this post. So secondhand info is better than none.
As far as I know the V6 rated "torque capacity" is as high as an '87 to '93 V8 T5. Suits me.
I've been told by a reliable transmission rebuilder that you can swap inputs between the older T5's and the V6's (except the rare "Cobra" T5). Not quite the same as trying it myself. I have enough bits around that I could. And probably should, so I'll have a backup T5 on deck or one ready for when the '69 gets to that point.
Another one for somewhere on the to-do list.