Trim tabs will work. Assuming you're using a prop, the much cheaper hydrofoil stabilizers that attach to the cavitation plate on the lower unit also work surprisingly well. I bought mine from Cabela's for about $50.
You looking for adjustable trim tabs like on a big boat or just an extension of the bottom surface? I was thinking about solid (non-adjustable) extensions off both sides of my 16' Lowe tunnel. I have seen several guide boats with extensions anywhere from 4" to 10" and have heard good things about the extra lift. I don't see why it wouldn't work.
I have a set of floatation pods welded on the back of my 16ft Jon. It adds 200lbs of floatation and will flatten out your ride alot! My 35Hyper sport Mud Buddy pushes me about 31mph now and my take of and draft are awsome. Go to the Fisher beavertail web site and you can order them there. about 300 a pair I think I paid.
I forgot to mention the 1860 G3 is powered by the Yamaha 90/65 Jet. I have seen some Jons with the extension of the bottom surface beyond the stern 8-12 inches or so. Some all the way across and some 12 inches or so in from each side. Surely it must help to prevent the stern from going deep on take off, which would help in shallow water and smaller creeks.
The add-on pontoons to the stern would add much needed flotation when the heavy 4 stroke outboards are used but they are so bulky that I think they would be cumbersome in tight situations.
My concern with welding the bottom extensions is with welding the .100 material. I guess if the guy knows what he is doing it should be ok. But is not adjustable...not sure if that is a big deal or not. At least with the regular trim tabs they are bolt on...and are adjustable...but more expensive also.
I talked to a boat repair/fabricator in Wasilla and he said he has welded on the extensions for about 40 guide boats, so am leaning that way.