well good on ypu ifn ya aint gonna give up on it
as far as the carb goes,hollies are easy as apple pie to overhaul
even if it still runs,after it caught on fie,its a good idea to overhaul it
the fire could have damaged the floats,needle and seats,and other little diaphragms and such
but that your call there,it may run great for long time yet wiht that carb
now you said it only did it that one time,does that mean catching fire
or does that mean the whole knocking spitting sputtering pinging only happened the one time?
yes it would be cheaper to get a used trans,however you dont know how long that used trans has been sitting in the junkyard
they may say "we just got it in 2 days a go",but they tell people stuff like this cause its what people like to hear
one big problem with a used trans is when they sit unused for a period of time
all the little tiny rubber seals and orings dry up like a popcorn fart and get brittle,then you put the trans in and it works great for a couple of weeks
then all of a sudden reverse/low goes out or something else happens and next thing ya know your pulling that sucker again and getting it over hauled
good luck,ifn ya need any input or advise feel free to holler at me