993 3.6 Intake valves on SC head need help

[Cheshire Cat]

Ok folks, seems like I`ve screwed up a bit (big time?)...
The story is, I have 82 SC heads, ported blah-blah-blah, for some reason (don`t ask) I thought that 50mm intake valves would be a good idea, so I got some. 50mm 8mm stem intake valves. Got the valves, guides etc, all sorted. At the point of assembly I`ve realized I can`t use my retainers with 8mm stem valves. Since 993 valves have their keepers closer to the end of the stem (8.8mm from the top) and original a bit further down (13.3mm) I can`t put them back together like that. So, what would be my best solution in this case?
1. 993 retainers? Not sure if they`ll fit.
2. New custom valves with the same stem length and diameter (keep 8mm) but with proper lock grooves (keepers repositioned)? Not sure if the retainers will fit.
3. New custom 50mm valves with 9mm stem (and plenty of work to re-machine guides etc)? Way too complicated.
4. Custom retainers? What exactly should be done to the design to utilize current valves etc?
I really need help.
Cheers

[burgermeister]

Why would 993 retainers not fit? I can see the valve spring height being off - though I would expect you would have nonstandard spring height specs to go with your setup anyway, so the valve springs would need non-standard shimming regardless. All just conjecture, I have zero experience doing what you're attempting to do.

I do however have 993 as well as 911 retainers & valves sitting around, so if I can help with pictures or dimensions let me know.