Taking oil pan off with engine in truck

[87Skier]

So I know this may be a little hard to directly answer because not every truck/engine combo is the same. So, I recently swapped a new motor into my Jimmy and it is leaking a lot of oil from the front of the engine. I can't tell exactly where it is coming from, but it is dripping from the lowest point where the oil pan and timing cover meet.

When I say a lot, I mean I may drive it about 30 or 40 miles and it loses almost a quart. The engine is a 1997 Vortec 350 motor, and while I had it out I put all new seals on, a new timing set and timing cover (not supposed to reuse the old one according to GM), but I ended up buying a cheaper aftermarket one and I think this is where my problem is coming from. The oil pan gasket is a 1 piece FelPro gasket.

So, my plan is to replace the timing cover (with a Dorman OE replacement), oil pan gasket, front main seal, and timing cover gaskets. Can this be done in the truck? Or does the motor need to come back out.

Also, should I be looking elsewhere for leaks?

Thanks!