Putting a headplate on an old mainsail

I searched and found nothing on head plates, here, and elsewhere, and I didn't know anywhere else to ask a yachting question or two, without bothering my local sail maker. I already bother him enough. I want to shorten my old storm main, seen in part 3 of my re-imagine heron saga. I want to make it short enough to hike it up the mast high, with the boom set so that short passengers sitting on the front seat don't need to worry about the boom booming their head. A jib or genoa will be the main driver probably, for idling about with smallish passenger people unfamiliar with yachting.

To do this, about 5-6 inches height needs removing off the top, no great loss of motive force there. My plan of uneducated guesswork is to sandwich the top at my desired height with raw aluminium sheet (self anodising), or stainless steel, depending on what thin stuff I can find, about 70-80mm wide, flare the lower and forward edges out to avoid sail cut/abrasion, file rounded all edges and corners, clamp all together with many vice grips, drill, and Pop rivet with monel rivets, I think I still have, and then peen the rivets more on the through side. Cut the excess fabric off the top, seal the threads with a cigarette lighter. Drill a hole at the top and use a brass swaged eye from a kit; or hard bolt a sister clip in a useful position. When all done, hammer the rivets a little more, and all done. This is not a show sail, this is a backyard DIY budget job, under the banner of research and development.

Does anybody here know how to do it properly ? That is my main question.
And apart from corrosion between dissimilar metals, is my guesswork methodology sound ?
For a ten foot long roughy anyway.
Should it have a fabric gusset or two added between the plates ?
Should I just get my long suffering sail maker to do it all ? My est. is $100 - $120 if done by a pro., for an old small sail - not worth it.

Any guidance and tips will be appreciated.

As a teaser for part 4 of ERO, (to be announced), I deliberately tried to sink my boat today, just pulled the mast over at the boat ramp, (cold cloudy misty day with no one there), and filled it up over the side, then bucket in another 100 L water, and climb in. It still floats with water 1 inch under the seats, rolls terribly, almost uncontrollable, but will not sink. She's a safe little boat.

 

I think your plans should work. A storm sail does not need a perfect shape anyway, so a few wrinkles won't matter.

 

Since you have a local sailmaker-

Buy a set of head boards from him.
Install them yourself.

 

Thanks for the assistance, job done pretty much as imagined.
Stainless plates 60mm X 210mm X 0.6mm - shaped, flared, smoothed, plate sized heavy sailcloth patches both sides of sail, all sandwiched with contact adhesive, pulled tight and clamped. Used 10 of 3/16 stainless rivets, broke my riveter on the second one (had a good spare), popped and peened tight, cut the top off the sail, bolted a sister clip on, done.
It's heavy and overkill, but 'free', and done now, not on a waiting list with a bill coming. I will tell all how it went in use in a few weeks time probably.

Maybe there's scope for another sub-category somewhere here, for information on sail care and maintenance, home repairs, and sail making information for DIY types. I and many others have an old sewing machine. Tips like - the best sail repair tape to use (I bought some rubbish); materials that don't go together well, or do go together; if contact adhesive adversely affects old dacron, etc. No laser cutting and computer design high tech stuff, but for old blokes with scissors, thimbles, and hand awls, and young folks with big ideas and no money. Just a thought.

 

Repairing sails with contact adhesive works OK, but eventually degrades with UV. However, I have patched really old crappy sails with it.