4 string pickups for 5 string

blades dont extend to the very end of the pickup. so the pickup cover is not necessarily a measure of the range of magnets.

give it a shot, it might work for you. but it wont work if its a jazz pickup because the screw ears wont match the routed cavity.
you can put in the 4strings pickup under the cover of the 5stringer pup if you want.

 

In my experience, yes, a blade design will work better.

My first 5 string was a Hamer Blitz bass that I special ordered way back when 5's were very rare (early 80's). Straight out of the box the A string seemed kinda weak. It was a J-J setup, the pickups did not have exposed pole pieces. It turned out that they had put a 4 pole pickup in the neck position, and a 5 pole in the bridge position, so if you dialed up 100% neck, 0% bridge, the A string was completely dead since it passed directly over the center of the pickups. I was really surprised/disappointed that Hamer had sent the bass out like that, but I swapped the pickups out for EMG's (blade design) and all was good.

Those pickups had a single pole for each string, though; more typical jazz pickups with two poles per string may have a wider magnetic aperature and may work a little better with the off-kilter spacing. But there's no shortage of proper 5 string pickups available, so I would just go with something you know will work properly.

Edited to add - there's a number of pickup manufacturers that make 5 string pickups that fit in a normal 4 string J pickup route. EMG (I think they call it a J-3.0) and Bartolini for sure, and I think Nordstrand and Aero also.

 

You will experience "dropout" without a 5 string p/u.
Peace

 

Four string Jazz single coils will work fine for narrow string spacing 5s, IME. Humbuckers with side by side coils will not. There is a magnetic null between the coils at the A string. Take good measurements of the pockets in your bass. Jazz PUs are made with several size and mounting screw location variations.