I recently purchased a 1987 monte carlo ss with a 400 cid sbc for me and my son to build together... I pulled the motor to rebuild and repaint etc. and I realized it has two different heads on it casting numbers

468642
462624

I checked on mortec and all they tell me is they are from 75- up 350-400 heads !
they look totally different to the eye right next to each other as for casting design , that's what caught my attention ! but bolted to the motor its not very noticeable
so my question would be are these heads ok to use together ,(they both have 1.94 intake and 1.5 exhaust valves) the car ran fine before I took it apart , or should I get a new set of matching heads , and which ones... its just a nice cruiser car with a little get up smoke the tires kinda deal... my son is 15 almost 16 and its his favorite car and going to be his driver... which heads should I go with 305, 350, or 400 ? I know about drilling the water jets on the 350s etc but I have not much experience building 400 motors just looking for some advice and direction so I get the best bang for my buck but want to keep it mainly close to stock it being his first car ! I have a 383 stoker sitting on my motor stand but he is not getting that !!! the block number is #3951509 400 sbc 2 bolt main( eldebrock intake with eldebrock 4 b carb normal distributor shorty headers) so keeping it close to stock with the basic pretty up visual stuff and performance upgrades .... which would be the best bet for my heads ? use what I got or ???? find new set and which ones?? thank you in advance for your advice and thoughts ....