Play at iron length with a heavy graphite or steel shaft (depending on your iron situation) and profit.
I've played many 19deg hybrids and had them all set up this way. Even have a 19deg Mizuno JPX 825 with a Project X steel shaft in it that I used to game regularly. Just switched to the 850 (with a heavy graphite) because I dig the blue head.
Looking at getting a Cobra F7 hybrid for fun. Would not consider playing it longer than 39" or with a graphite shaft lighter than 80g.
If you put an iron head on a ridiculously long, light shaft you'd not have any fun either. If they're iron replacements, treat them as such. My hybrid off the tee is almost as reliable as my 4i.
May need tip weight depending on natural head weight of the hybrid if you're going shorter and heavier. If the stock length is 42" and you're playing 39" be smart about it.