motor swap

[292farmer]

ok so i want to pull out the 292 in my truck so i can rebluid it and want to install another motor in it to keep it running and useable. i havent found another inline that runs the only one i found locally in my area was pulled out of a truck 15yrs ago and was stored in a jeep wagon, and the guy wants 500-600$ firm...so out of the question for me.how ever i found a 305 v6 and a 283 v8 the 305 is from a 61 gmc and the 283 is from a 57 chevy truck, both run and are both 500 obo
so i know the right side passenger mount is moved forward on my 292, but will i be able to use the drivers side or will i need all new mounts? which would bolt in easier? i have the sm465 my truck is a 3/4ton so im not sure weight on 292 but i know the 305 is about 650lbs so i might sink a little? would either one bolt to my bellhousing with out requiring movement/replacement of my tranny or use of an adapter?
i believe the 283 shares the 292 bolt pattern but im unsure and idk about the 305. both were hooked to manual trannys before. also the both motor came with trannys if i want should i do that? both are 4 spd so im guessing their the sm420? would that make my job easier?
sorry this is so long i searched threads but whilei found mention of swaps from v6 to v8 and vice versathey all included tranny swaps, which doesnt help much with my idea of bolting to same tranny. any advice please thanks