Not much luck finding a bigger boat to fit my needs but got a free 15 foot in great shape but it's riveted I'm wanting to mount my 27 prodrive on something would it be worth having a welder weld this boat up for me or will it not hold up ?

It's not gonna last.

Unless it's leaking bad already, don't bother welding it up yet. That's just wasting cash. Put your motor on and run the chit out of it and save your money for it's replacement.

X2^^

X3^^^
I bucked all the rivets and beefed up the transom on my early 80's flat 1648. Plopped my 27 mini on the back 3 years ago, and it still is problem free. just gotta re-buck the gunnel rIvets once a year. Its about tIme to retIre thIs boat and get a phowler, It has taken a beatIng. So Ya, it'll work, for a while.

What's all involved in beefin the transom To be good enough for my 27 prodrive I'm not that hard on a boat jump a few banks from time to time to get in fishing an hunting holes never just for fun something I could do at home or should I bring to to someone ?

I pulled the wood and braces out, and welded some 2x4 aluminum tubing in like you see In most of these mud hulls.
This is how mine ended up coming out, should give you an idea, rock solid.

Thanks for the picture there's a boat builder right down the road from my house I will run it by him see if he can do something like this

If you can get away with it, tying the transom to the rear seat really beefs it up too.

There is only a folding set that is mounted to the side so I'm thing this will make it real easy to brace it up .... So it the transom is braced up well to what extent should I worry about the rest of the boat like floor sides stuff like that keep in mind Im not hard on boats only have one bank I cross to fish an frog witch is about 4 foot wide other thank that just open water an some shollowes