You can have it TIG welded. I`ve done this many times on trannys with no ill effects. As for the vibration what motor is it supposed to be? Did you buy the car complete or put the motor in yourself? Many yrs ago I bought a motor from a Judge`s kid that kept getting into trouble and wanted something else to calm the car down. It was supposed to be a 428 cj which I confirmed buy the local shop who put the motor in for him. Long story short, wrong flex plate, I installed it with my 390 plate and had the 1800-2000 vibration. Changed out the plate for a 428 and no vibe. Is your motor what you think it is? Stranger things have happened.
It was supposed to be a 390. The car is a 390GT clone of sorts, so i knew it was no numbers matching kind of car. Bought it on Ebay couple of states away. At 53 yrs old, I need to stop being so trusting!
The block has the truck reverse 105 on the front. Is there any other numbers on the block to tell me what it is?
You should check the stroke with a piece of wire through the sparkplug hole. If it's a 390 with a 428 crank (410 cu ") you need to use the 428 plate, not the 390. Also, there should be a ring between the flex plate and the bolts to spread the load (I think!). I do know that the flax plates can crack from the bolt holes if left off.