SKYDIVER

bare with me boys and help a girl out out please. My dad has had this car a 1965 mustang in his garage for 28 years it is completly restored with a pony interior nice paint job looks great, he drove it 4 years ago and it blew a freeze plug. its a 1965 mustang with 300 miles on a rebuilt engine. it has a 289, been bored out 30 over pistons, headers, a blower. he replaced it with a rubber freeze plug. Dad gave me the car and I got it running no problem but the same freeze plug blew out after i drove it about a one mile. I have been given a lot of conflicting advice rubber freeze plug brass freezeplug etc. It is not easy to get to it is next to the motor mount what is best advice? do i have to take the engine out to replace with metal?