6 cyl to V-8 Swap Oil Pan issue

LISTEN TO ME
You can put a 351 in a '65, with some issues. 1) VERY limited as to what headers to use, 2) Issues if you try to install power brakes, 3)Weight....

I studied...much. I was rebuilding the 289 in my '65 and was thinking of putting a 351W in instead. After much reading, I wasn't putting up with the headaches. It has been done a lot. But, the 302 will fit easier and allow you more options. You can get 350hp out of that motor. Also, if you're wanting that power, you need to change suspension, steering, brakes, etc. If you haven't already, look at "converting" it to a v8. Yes, this means rearend, driveshaft, front end, etc.
Been there done that. Don't just build a 351 'cause it's bigger unless you know what you're in for. '65-'66 cars don't have the space the '67s and up do.

BTW, 289/302--front sump---WAIT-see below

Can't really help you there. I didn't have any rust issues on the frame, floors, etc....1 in a million I guess. I will be adding subframe connectors down the road. Sorry. Seriously though, if you want to avoid headaches, stick with a 289/302. 351W is doable, just limited as to what you can do. I literally found 1 set of headers that will fit a 351W going in a 65-66. That is just the start. I'm running a 289, 0.040, Edelbrock Performer package (cam, intake, carb), built '69 302 heads, with Hedman Elites, all new guts, standard 3 core radiator w/stock fan + shroud, going through a c4 and I'm guessing (not dynoed yet) around 300hp. That is a pretty mild build. Post a thread titled, "Best way to get 350-400hp out of a 289/302" and some more experienced engine guys will chime in. Plenty of people doing it. Mine runs very nice with my 2.79 rear. The 3.55's are on their way....zoom zoom

Good luck and let me know if I can help. I'll answer what I can.

Oh yeah, I need to double check 'cause I'm thinking it's a rear sump. I'm confused, I'll let you know--duh

You have to have a front sump.

Also the 351w is physically bigger than a 302.

Use a front sump oil pan. It is your choice to go 302 or 351w. About the only main difficulty is that you need special swap headers. There are a few different suppliers of these, although none of them fit great in a 65/66 engine bay so some tinkering needs to be done. You will also need to screw with brackets which are different than the 289/302 and update the radiator.

Here is a pic of the 351 stroker in my 65: