Child seats for 2 year old - options?

[Big D]

I getting ready to put in 3 point belts in my 72. I would like to also like to do something for the middle seat. I,ve got a Simpson 6 point race belt out of a stock car but I have not figured a good way to mount the shoulder straps since i"m still running the cab mounted tank.

Both my kids are now in booster seats. It says in the manual for the last one I purchased that shoulder belts are preferred for booster seats. I may be a little overzelous when it comes to safety but there is a lot of steel in the dash of these trucks.