Would a mercruiser 502 intake bolt right into a jasper 502? Would i be able to use all my accessories off my mercruiser motor fit the jasper 502 the same? Would the jasper motor bolt into my 1990 250 sport baja the same as my 502?

Yes, yes, and yes.

I will that jasper 502 motor be the 425 hp as well? Or is it more?

Not sure what they rate HP at. Merc carbed 502 was rated at 390hp

I have 2 merc 502 mag intakes and crabs. Reach out if interested and I will get you some pics.

Yes on all

Yes on the intake. I am no expert however I was told not all 502s are setup for mechanical fuel pumps.