Amplifiers will have a "minimum tolerance level" for the load presented to the output...this is made up of the nominal reistance of the speaker cabinet plus the resistive load of the cabling.
It would be unusual for even a HiFi amp to only drive down to 8ohms unless it is a valve design.
However, if that is what you have, then no, you cannot drive 4ohm (nominal) speakers from an amp with a minimum tolerance of 8ohms.
The way round is, as MickeyBlue says is to use a single channel and wire the 2 cabs in series...
That is positive from the amp to positive on the 1st cab...negative on the 1st cab to positive on the 2nd cab...negative on the 2nd cab to negative on the amp...Obviously you only get one channel and the (one channel) power is divided between the 2 speakers...
I'd say buy a cheap but modern studio amp....Samson do a range around the £100 quid mark or check out eBay