The iteration of this probe for any camera is the Sinar Booster 1. It has a lightweight cassette that takes the position of the film holder, into which the probe is inserted. These things are best suited for the studio. Advantages of using the probe are automatic bellows compensation, on axis metering (hand metering requires readings from the side of the camera which could be less accurate), reading through filters,and spot flash metering which will prove accurate even if your aperture scale is off.
One option with the Sinar Booster is to use it with the Sekonic L508 rather than the Minolta IV or V - these meters have a compatible accessory cell system. The L508 gives you the possibility of spot metering albeit without a viewfinder readout. You can also use the Minolta Booster II to give a very sensitive system (Sekonic/Minolta combination shown in picture - it can read quite accurately down to at least EV -8 at ISO 100, as shown). The later Sekonic spot/incident meters (558, 758) have viewfinder readout but no accessory socket. They also added independent spot/incident calibration, which the 508 does not have.
Perhaps a little late in the day to add, but atleast for ambient and flash I'd recommend the Minolta V flashmeter. Quite straight forward to use, and runs on a common as muck AA battery that seems to last ages - I've had the meter for five or six years, and it was last August I had to replace the battery for the first time.
That said, I've just spent £320 on the Sekonic 758D, as I begin to use 5x4 more often outdoors, I notice I need the use of a spotmeter. Only real reason I went with a new one was there was about £50-60 difference in price for a second hand older model that only had a 12 month warranty. Being in the UK, the sale of goods and services act covers a new item pretty much like an extended warranty.